Measuring a door sounds like the simplest job in the house, and it is the one that goes wrong most often. Almost every returned door we deal with comes back for one of four reasons: somebody measured the old door rather than the opening, somebody measured in only one place, somebody forgot that the lining takes up space, or somebody ordered a metric size for an imperial opening. All four are avoidable in about ten minutes with a tape measure and a spirit level.
This guide sets out exactly what to measure, the standard UK sizes you are trying to land on, the gaps a door actually needs, how to measure ironmongery, and the eight mistakes that cause the most trouble. Doors2Floors has supplied doors and flooring to homes and businesses across the UK, and we stock over 710 internal doors from £30.84 and over 90 external doors from £86.79, so the sizes quoted here are the real ones our doors are actually made in.
What you actually need to measure
Three dimensions, not two
Height, width and thickness. Thickness is the one people skip and it is the one that decides whether your existing hinges, latch and handles will fit at all.
Height
Measure from the finished floor to the underside of the head of the lining. Take it on the left, in the middle and on the right, and use the smallest figure.
Width
Measure between the two lining faces at the top, at the middle and near the bottom. Use the smallest figure again.
Thickness
Measure the leaf edge with the door open. Standard UK internal doors are 35mm. Fire doors are usually 44mm or 54mm. External doors are commonly 44mm.
Whether the opening is square
Measure both diagonals across the opening. If they differ by more than a few millimetres, the opening is out of square and you need to know that before you order.
Whether the opening is plumb
Hold a long level against each side of the lining. A lining that leans will make a correctly sized door bind at the top or the bottom of the closing edge.
Which way it opens and which side is hinged
Stand outside the room looking in. If the hinges are on your left it is a left hand door. Getting this wrong matters on any door that is not symmetrical, and on every fire door and external door.
What is on the floor
Note the existing floor finish and whether it is changing. New flooring under a door changes the height you need, and it is the reason a door that fitted perfectly last month now catches.
Write everything down
Six measurements per opening, plus the diagonals, plus the hand and the thickness. Doing it from memory across five doors is how two of them end up wrong.
Standard UK door sizes
Britain uses two size systems at once
Imperial sizes, quoted in millimetres but derived from inches, and metric sizes. They are not interchangeable and mixing them up is the most common ordering error in the country.
Imperial internal door sizes
All at 1981mm high, which is 78 inches. The widths are 457mm (18 inches), 533mm (21 inches), 610mm (24 inches), 686mm (27 inches), 711mm (28 inches), 762mm (30 inches), 813mm (32 inches) and 838mm (33 inches).
Metric internal door sizes
All at 2040mm high. The widths are 526mm, 626mm, 726mm, 826mm and 926mm.
How to tell which system your house uses
Measure the height of an existing door. Around 1981mm means imperial. Around 2040mm means metric. Houses built or refurbished from roughly the 1970s onwards are more likely to be metric, but there is no reliable rule and you must measure.
What the prices look like across a range
Price usually rises with width. Our LPD White Primed Flush internal door runs from £30.84 at 1981mm x 457mm up to £44.75 at 1981mm x 838mm, which gives you a sense of how the increments work within one pattern.
Fire door sizes
Our LPD White Primed Flush FD30 door is available at 1981mm x 533mm, 610mm, 686mm, 762mm and 838mm, and at 2040mm x 526mm, 626mm, 726mm, 826mm and 926mm. It starts at £87.39 in the metric sizes and is £92.29 across the imperial widths. We stock over 240 fire doors in total, including over 150 FD30 fire doors and 8 FD60 fire doors.
The most common sizes in British houses
762mm x 1981mm is the standard main room door in an imperial house. 686mm x 1981mm is the standard for smaller rooms and bathrooms. 826mm x 2040mm is the most common metric main room size.
Narrow doors
457mm and 533mm imperial widths are used for cupboards, airing cupboards and very tight cloakrooms. They are real doors, not made to order specials.
Pair widths are quoted differently
A French pair or a divider is quoted by the OVERALL width of the pair, not per leaf. Our 3 French door pairs from £407.44 come in overall widths of 914mm, 1067mm, 1168mm, 1219mm, 1371mm and 1524mm at 1981mm high. Our French doors guide explains this in detail.
Full size reference
Our dedicated guide to UK internal door sizes lists every size with its imperial equivalent.
How to measure an existing door for replacement
If you are keeping the lining and simply swapping the leaf, this is the quicker route. It is also the route where measuring the old door alone will let you down.
Take the old door off if you can
Lay it flat and measure it properly. Measuring a hung door means measuring around a frame and it introduces error.
Measure the old door height at both edges
The hinge edge and the closing edge. If they differ, the door was trimmed on site, which tells you the opening is out of square.
Measure the old door width at top, middle and bottom
Same reasoning. A door that tapers by 5mm was scribed to fit a leaning lining.
Measure the thickness
35mm, 44mm or 54mm are the usual answers. If you are replacing a 44mm door with a 35mm one, your latch, hinges and handle spindle will all need attention.
Then measure the opening as well
This is the step people skip. If the old door was trimmed, its dimensions are not the size you want to order. The opening tells you the truth.
Work out whether the old door was cut down
Compare the old door to the standard size list. If it is 755mm wide, it started life as a 762mm door and somebody took 7mm off. Order the 762mm and trim it the same way, or order the size that suits the opening.
Note the hinge positions
Measure from the top of the door to the top of each hinge recess. If you want to reuse the existing recesses in the lining, the new door has to be recessed in the same places.
Note the latch height and backset
Measure from the floor to the centre of the spindle hole, and from the door edge to the centre of the spindle hole. That second figure is the backset, and it is usually 44mm or 57mm.
Photograph the old door before it goes
The pattern, the number of panels, the glazing and the hardware positions. It is a two second job that saves a lot of guessing.
Check the finish you are matching
If you are replacing one door out of six, the new leaf has to match the other five. Our guides to door finishes and internal door finishes cover matching, and we stock over 350 fully finished internal doors and over 80 unfinished internal doors.
How to measure the opening for a new lining
If you are forming a new opening, or replacing the lining as well as the door, you measure the structural opening and work inwards.
Measure the structural opening
The brickwork, blockwork or stud opening, before any lining goes in. Width and height, in three places each.
Subtract the lining thickness twice
A lining sits on both sides of the opening. Whatever the lining material thickness is, you lose it twice from the width and once from the height.
Then subtract the clearance gaps
The door needs a gap at each jamb and at the head. Only then do you arrive at the door size.
Work out the lining width you need
Lining width equals the wall thickness plus any plaster or plasterboard on both faces. A lining that is too narrow leaves a step. A lining that is too wide has to be planed flush after fitting.
Allow for the floor finish
If the floor is not down yet, the lining has to be set from the FINISHED floor level, not the subfloor. Getting this wrong is why a lining sometimes finishes 15mm short.
Check the head is level and the jambs are plumb
Fix the lining plumb and square even if the opening is not, and pack behind it. The lining is your chance to correct the building.
Do not force a lining into a tight opening
A lining squeezed into an undersized opening will bow, and a bowed lining makes a straight door look bent. Ease the opening instead.
What we stock
We list over 30 internal frames and linings and 2 external frames, plus 16 architrave products. Our guide to door architraves covers the trim that finishes the junction.
Structural openings need care
Forming a new opening in a loadbearing wall, or widening an existing one, is structural work. Get advice from a structural engineer or your local building control body before cutting anything.
The gaps and clearances a door needs
Why the gaps exist
A door needs clearance to swing without binding, to allow for seasonal movement in the timber, and to allow for a floor finish that is not perfectly flat. A door fitted with no gaps will bind in the first damp week.
The sides and the top
A small even gap down each jamb and across the head. Consistency matters more than the exact figure, because an even gap is what makes a door look properly hung.
The bottom
The bottom gap is the biggest, because it has to clear the floor finish, any threshold bar and any carpet. It is also the gap where draughts and noise get through, which is a genuine trade off.
Bottom gap and carpet
If a carpet is going down after the door, the bottom gap has to clear the carpet plus the underlay plus the gripper. Measuring this before the carpet is fitted is guesswork, so ask the carpet fitter for the total build up.
Bottom gap and hard flooring
Engineered wood, laminate and LVT with underlay all raise the floor. Our guides to engineered oak flooring, laminate flooring mistakes and Karndean flooring cover the build up, and we stock 12 flooring products from £14.00 per square metre.
Fire doors have their own gap requirements
Gaps around a fire door are part of what was tested, and the threshold gap in particular must not be blocked or enlarged on assumption. Confirm the correct gaps for your specific door with the manufacturer, your local building control body or a fire risk assessor.
Draughts versus clearance
A generous bottom gap is a draught. A brush seal or a threshold strip closes it without making the door bind. Our guide to draughty doors covers the options, but never block ventilation serving a gas or solid fuel appliance.
How much can you trim?
Most solid and engineered doors allow a modest trim from each edge, but the allowance is set by the manufacturer and it is much smaller on a glazed door, a hollow core door or a fire door. Check before you cut. Our guides on planing a door and hollow core versus solid core doors explain why.
Never trim a fire door on assumption
Cutting or planing beyond the certified allowance can take a fire door outside the scope of its certification. If you need a size that requires more than the permitted trim, order the correct size.
How to measure door ironmongery correctly
Hinges: measure the leaf length and the width open
A hinge is described by its leaf length first, then the total width when the hinge is laid open flat. A 76mm x 50mm hinge has 76mm leaves and measures 50mm across when open.
Hinge knuckle position
Measure from the top of the door to the top of the hinge and from the bottom of the door to the bottom of the lowest hinge. Reusing existing recesses means matching both.
How many hinges
Two for a light internal door, three for anything heavy, glazed or fire rated. We list over 350 door hinge products, over 20 butt hinges from £5.61, over 40 concealed hinges and over 50 fire rated hinges from £8.99. Our guide on where to fit door hinges covers positioning.
Latch backset
Measured from the face of the door edge to the centre of the follower, which is the square hole the spindle passes through. Common UK backsets are 44mm and 57mm, and they are not interchangeable because the handle rose sits in a different place.
Latch case length
Sometimes quoted as 64mm or 76mm, referring to the overall case. Matching the case length matters if you are reusing an existing mortice in the door edge.
Spindle length
Door thickness plus the depth of both roses or backplates, plus a couple of millimetres. This is why a 44mm fire door needs a longer spindle than a 35mm internal door, and why swapping door thickness means swapping spindles.
Handle rose diameter and fixing centres
If you are replacing handles and want to cover the old fixing holes, measure the existing rose diameter and the distance between its fixing screws. Our over 280 handle packs start at £8.99 within over 2,500 door handle products, and our door handles guide covers selection.
Lock centres on a backplate
The distance between the centre of the spindle and the centre of the keyhole or thumbturn. Get this wrong and the lock case will not line up with the plate. We list over 210 handles on backplate, over 720 locks and latches from £1.92 and over 60 bathroom locks from £6.64.
Strike plate position
Measure from the finished floor to the centre of the latch bolt with the door closed, then transfer that to the lining. A strike plate 3mm out is a door that rattles.
Letter plate aperture
On an external door, measure the aperture rather than the visible plate. The plate overlaps the hole, so the two figures are different.
Door closers and stops
Closers are sized by door width and weight, not by opening. We list 4 door closers from £95.50 and over 30 door stops from £10.88.
Check what will still fit before you change thickness
Changing from 35mm to 44mm affects the spindle, potentially the hinges, and the lining rebate. It is not just a door swap. Our notes on fixing a loose door handle explain how the parts relate to each other.
Measuring less common door types
Fire doors
Measure as normal, but understand that you are buying into a certified assembly. The leaf, frame, hinges, seals, latch and any glazing were tested together. Our overview of fire doors and where they are needed and our notes on fire door materials cover the construction, and requirements should be confirmed with your local building control body or a fire risk assessor.
French pairs and room dividers
Quoted by overall pair width. A 1219mm pair is two leaves of roughly 610mm each. Our 17 room dividers from £498.06 include fixed side panels, so measure the whole opening.
Bi-fold doors
Measured by the opening they fill, and the number of leaves determines how much stacking depth you lose at the side. We list 15 bi-fold doors from £131.35, and our guides on how bi-folds work, bi-fold door ideas and bi-folding door costs cover the detail.
Pocket doors
You need the opening width and roughly twice that width of clear stud cavity for the door to slide into, with no services in it. We list 4 pocket doors.
Sliding doors on a track
Measure the opening, then check you have the same width again of clear wall for the leaf to slide across, plus room for the track. We stock 16 sliding door kit systems.
Stable doors
Split horizontally into two independently opening halves, so measure the opening and note where you want the split. Our stable doors guide covers the format.
Ladder doors and loft hatches
Measured to the finished opening. We list 2 ladder doors.
Glazed doors
Measure as normal, but note that the trimming allowance is far smaller because the stiles and rails are narrow. We stock over 280 glazed doors from £107.25 and over 420 unglazed doors from £30.84.
Cupboard and wardrobe doors
Often narrower than any standard door, and frequently a pair. Our 457mm and 533mm imperial widths cover most cupboard openings.
External doors
Measure the frame opening as well as the leaf, because an external door is usually supplied to suit a frame with a threshold. Our over 90 external doors start at £86.79, with over 30 glazed external doors from £274.81 and 18 composite external doors from £725.00, each of which has its own individual measured size.
Doors for a sloping or uneven floor
Measure the height at both edges and expect to scribe the bottom edge. Do not simply order the taller figure and force it.
Measuring a whole house of doors
Replacing every internal door at once is much cheaper per door than doing them one at a time, but it multiplies the measuring risk. A systematic approach removes almost all of it.
Draw a simple floor plan first
Sketch each floor and number every opening. You are going to refer back to this repeatedly, and numbered openings stop you confusing the two bedroom doors.
Make a table, not a list
One row per opening, with columns for height at three points, width at three points, thickness, hand, hinge positions, latch height and any notes. A list of loose numbers becomes meaningless within a day.
Expect a mixture of sizes
A typical extended British house has main room doors at one size, bathroom and small bedroom doors at a narrower size, and cupboard doors narrower again. Three or four different sizes across one house is normal.
Group the openings by size
Once you have the table, group identical openings. This is what lets you order confidently and spot the odd one out.
Identify the awkward one early
There is almost always one opening that does not match anything, usually under the stairs or into a loft conversion. Deal with that one separately rather than letting it hold up the whole order.
Decide on a single pattern and finish
A house reads as coherent when every door is the same pattern. Our guides to choosing internal doors for modern UK homes and the most popular internal door styles cover the choice, and we stock over 420 unglazed doors from £30.84 and over 280 glazed doors from £107.25 in matching patterns.
Plan which doors get glazing
Hall, kitchen and any dark room benefit from a glazed leaf in the same pattern as the solid ones. Bathrooms and bedrooms do not.
Order all the hardware together
Five doors is ten handles, twelve to fifteen hinges and five latches. Ordering it in one go guarantees the finishes match. Our over 280 handle packs from £8.99 and over 2,900 door hardware products cover the whole house.
Check which openings need a fire door
Integral garages, loft conversion escape routes and flat entrances are the usual cases in a house. Establish this before you order anything, because it changes the thickness and therefore the hardware.
Budget the fitting
A joiner hanging six doors in one visit is far cheaper per door than six separate visits. Our notes on internal door fitting costs explain how this is usually priced.
How door construction affects what you can measure and cut
Solid core doors
A dense core throughout, heavier, better acoustically, and with the most generous trimming allowance because there is solid material at the edges.
Hollow core doors
A thin facing over a lattice core with solid lock blocks. Trimming allowance is small, and cutting into a lattice area leaves nothing for a hinge or latch to bite into. Our comparison of hollow core and solid core doors covers the difference.
Engineered core doors
A stable engineered core with a veneer or primed facing. The most common construction in quality modern doors and the least likely to warp.
Where the lock block sits
On a hollow core door the lock block is a solid section on the closing edge, usually around handle height. Trimming a hollow core door significantly can move the block out of position relative to the new door height.
Glazed doors and narrow stiles
A glazed leaf has narrow stiles and rails and very little to remove. Measure carefully and do not plan on trimming much.
Fire door cores
A fire door core is a specific tested material and the certified trimming allowance is usually small. Never exceed it. Our notes on fire door materials explain the construction.
Primed versus fully finished and measuring
A fully finished door that you trim will have a raw cut edge that must be sealed. A primed door you were going to paint anyway does not care. Our guide to pre-finished, unfinished and primed doors weighs it up.
Material and seasonal movement
Timber doors move with humidity, engineered cores move much less, and that movement is exactly what the clearance gaps are for. Our guide to internal door materials covers how each behaves, and we stock over 290 oak, over 30 walnut, 6 pine and over 20 laminated internal doors.
Measuring in awkward locations
Under the stairs
Almost always non standard and frequently cut on a rake. Measure the height on both edges and record the angle, and expect to scribe.
Loft conversions
Head height at the top of the stairs is often restricted, and there may be fire separation requirements on the escape route. Measure, then check the regulatory position with your local building control body before ordering.
Integral garage doorways
The door between a garage and a house typically has fire and threshold requirements. Measure normally, but confirm the specification before you order.
Cellars and basements
Low heads, uneven floors and often damp. Measure the height in several places and deal with any damp before you fit a timber door.
Bathrooms with a raised threshold
Wet room formers and tiled thresholds raise the floor considerably. Measure to the finished tile, not the screed.
Airing and boiler cupboards
Narrow, and sometimes needing ventilation. Do not fit a fully sealed door where ventilation is required, and never obstruct ventilation serving a gas or solid fuel appliance.
Where a radiator is behind the door
Measure the swing clearance as well as the opening. A door that fits the opening but hits a radiator is still the wrong door.
Period properties with settled openings
Victorian and older openings are frequently out of square by a noticeable margin. Measure the diagonals and plan to correct it in the lining. In a listed building, check with your local planning authority before altering an opening or replacing an original door.
Very tall Victorian openings
Some period openings are taller than any standard door. Options are a made to measure leaf, a fixed panel above the door, or a fanlight, and the last two are usually cheaper and more sympathetic.
A measuring checklist you can work through
Before you start
Steel tape, long level, pencil, notepad, torch, and a sketch of the floor plan with every opening numbered.
For every opening, record
Height left, height middle, height right. Width top, width middle, width bottom. Both diagonals. Existing door thickness. Hand and swing direction.
Then record
Hinge positions from the top and bottom of the leaf, latch height from the floor, and the latch backset from the door edge.
Then note
The existing floor finish, whether it is changing, and the total build up if new flooring is going down.
Then check
Whether the opening has any fire, escape or ventilation function, and whether the property has any listed, conservation or leasehold restrictions.
Then decide
Which standard size each opening is aiming at, whether it needs trimming, and whether the lining needs adjusting.
Finally
Send us the table before you order. It costs nothing to have a second pair of eyes on thirty numbers, and it is the cheapest insurance available on the whole project.
The tools you need, and the ones that help
A steel tape measure, not a fabric one
A fabric tape sags and stretches. A 5m steel tape with a locking blade is the right tool.
A long spirit level
1.8m if you can, because a short level will not tell you whether a 2m lining is plumb.
A pencil and a notepad
Write every figure down against a sketch of the opening. Six numbers per door and five doors is thirty numbers.
A digital caliper or a rule for thickness
Measuring 35mm versus 44mm with a tape hooked over an edge is surprisingly error prone.
A laser measure for the diagonals
Not essential, but it makes checking squareness a one person job.
A torch
Lining heads and hinge recesses are usually in shadow.
Somebody to hold the other end
For anything above about 2m, two people is faster and more accurate than one person and a bent tape.
Eight measuring mistakes to avoid
One: measuring the old door instead of the opening
If the old door was trimmed on site, its size is not the size you want. Always measure both.
Two: measuring in one place only
British openings are not square. One measurement tells you nothing about the other end.
Three: forgetting the thickness
Thickness decides your spindle length, your hinge choice and whether the lining rebate suits.
Four: mixing imperial and metric
An 826mm x 2040mm metric door in a 1981mm imperial opening is 59mm too tall. It is not a trimming job.
Five: measuring from the subfloor
Measure from the FINISHED floor level, including any flooring still to be laid. This is the single most expensive mistake to correct after the fact.
Six: ignoring the diagonals
An out of square opening needs to be corrected in the lining, not absorbed by the door. Knowing it in advance is what lets you plan for it.
Seven: forgetting which way it opens
Hand and swing direction matter on any non symmetrical door, and on every fire door and external door.
Eight: assuming all doors in a house are the same size
They very often are not, particularly in an extended or refurbished house. Measure every single opening.
The bonus mistake: rounding
Write down 762mm, not "about 760". Rounding to the nearest 10mm loses exactly the information you need.
What to do when no standard size fits
First, check whether trimming will get you there
If you are within the manufacturer trimming allowance, order the next size up and trim it. This is the cheapest and most common answer.
Second, consider changing the lining rather than the door
Adjusting or replacing the lining is often easier than sourcing a non standard leaf, and it gives you a plumb square opening as a bonus.
Third, consider packing the lining out
If the opening is slightly too wide, a packing piece behind the lining brings it in without any structural work.
Fourth, look at a different format
A very wide opening may suit a pair, a divider or a sliding leaf better than a made to measure single door. Our guide to choosing the right door works through the formats.
Fifth, made to measure
Genuinely bespoke doors exist but they cost considerably more and take longer. Exhaust the four options above first.
Never solve it by over trimming a fire door
If a fire door will not fit within its permitted trim, the answer is a different door, not a bigger saw cut.
Clearance and budget options
If you are flexible on pattern, our over 20 clearance doors from £53.00 and our guide to the UK's cheapest internal doors are worth a look.
Frequently asked questions
What is the standard door size in the UK?
There are two standards. Imperial doors are 1981mm high with widths from 457mm to 838mm. Metric doors are 2040mm high with widths from 526mm to 926mm. 762mm x 1981mm and 826mm x 2040mm are the most common main room sizes.
Do I measure the door or the frame?
Measure both. The opening tells you what will fit and the old door tells you what was there, and they are frequently different because the old door was trimmed.
How do I know if my doors are imperial or metric?
Measure the height of an existing door. Around 1981mm is imperial and around 2040mm is metric. Never assume from the age of the house.
How much gap should there be around a door?
A small consistent gap at both jambs and the head, and a larger gap at the bottom to clear the floor finish. Even gaps matter more than any exact figure, and fire doors have their own tested gaps that should be confirmed for that specific door.
Can I cut a door down to size?
Usually a little, within the manufacturer allowance, and the allowance is much smaller on glazed, hollow core and fire doors. Never cut a fire door beyond its certified allowance.
Which side is the hinge side?
Stand outside the room looking in. Hinges on your left is a left hand door, hinges on your right is a right hand door.
What is a door backset?
The distance from the door edge to the centre of the spindle hole, usually 44mm or 57mm in the UK. It determines where the handle sits.
How thick is a standard internal door?
35mm for a standard UK internal door. Fire doors are usually 44mm or 54mm, and external doors are commonly 44mm.
Do I need to measure every door in the house?
Yes. Houses that have been extended, converted or refurbished very often have a mixture of sizes, and assuming uniformity is a reliable way to order one wrong door.
What if my floor is not level?
Measure the height at both edges of the opening, order to the larger figure if it is within the trimming allowance, and scribe the bottom edge to the floor.
How do I measure for a French door pair?
Measure the structural opening, then work back through the lining and the gaps to the overall pair width. Remember the quoted width is for the pair, not per leaf.
Should I measure before or after new flooring?
Ideally after, or with a confirmed finished floor level from the flooring fitter. Measuring from a bare subfloor and hoping is the most common cause of a door that catches.
What does the fitting cost?
Our notes on what it costs to fit an internal door explain how joiners usually price the work, and why accurate measuring reduces it.
Can you check my measurements?
Yes. Send us the figures before you order and we will tell you which standard size you are aiming at.
Getting it right first time
Doors2Floors has supplied doors and flooring to homes and businesses across the UK. We stock over 710 internal doors from £30.84, over 290 internal oak doors from £87.75, over 80 white primed internal doors from £30.84, over 240 fire doors from £87.39, over 90 external doors from £86.79, over 30 frames and linings, 16 architraves and over 2,900 door hardware products. Our ranges include over 500 LPD products, over 250 Deanta products and over 30 Mendes products.
Related guides
- UK internal door sizes explained
- How to choose the right door for your UK home
- How to plane a door
- How to stop doors swelling and sticking
- Where to fit door hinges
- How to fix a loose door handle
- A guide to door architraves
- French doors: the complete UK guide
- How bi-fold doors work
- Stable doors explained
- Fire doors: what, why and where
- Hollow core versus solid core internal doors
- What it costs to fit an internal door
- How to deal with draughty doors
Still not sure?
If your figures do not land neatly on a standard size, get in touch with our team with the opening width and height in three places each, the thickness of the existing door and which way it opens. Nine times out of ten there is a standard size that works, and it is far cheaper than a bespoke leaf.
Which sizes can I actually order?
Every width and height we stock is set out in imperial and metric in the door size guide.
Product counts, sizes and prices shown here are correct at the time of writing and are subject to change. Trimming allowances are set by the door manufacturer and should be checked for your specific door. Fire door sizes, gaps and permitted alterations form part of a certified assembly, so confirm anything specific with your local building control body, a fire risk assessor or another competent professional. Forming or widening a structural opening is building work and may require structural advice.