Front door sizes and standards

Four different numbers get called "the door size" on the same job, and they differ by up to 4 in (100 mm). The leaf is one number, the frame is another, the structural opening is a third, and the width you can actually carry a sofa through is a fourth and always the smallest. Everything else on this page is downstream of getting those four straight, which is why the entryway section starts here rather than with furniture.

The four sizes, and which face each is measured from#

The leaf is the slab itself, measured across its faces at the widest point, and across its long edges from head to foot. A US 36 x 80 in door really is 36 x 80 in, unlike a two-by-four. A UK 838 x 1,981 mm door really is that too.

The frame is the leaf plus clearance plus jamb stock. A pre-hung unit puts a 3/4 in (19 mm) jamb on each side and about 1/8 in (3 mm) of gap between the leaf edge and the jamb, so the outside of a 36 in doorset measures roughly 37.75 in (959 mm).

The rough opening is the hole in the framing, and it is the frame plus shim space: about 1/4 in (6 mm) each side and the same at the head. For a 36 x 80 in leaf that gives 38 x 82.5 in (965 x 2,096 mm), and the arithmetic behind it runs 36 + 0.75 + 0.75 + 0.25 + 0.25 = 38. The same logic drives every other size in the rough opening sizes table.

The clear width is what is left when the leaf is standing open at 90 degrees inside the opening. Between the jamb faces you have about 36.25 in. Take off the 1.75 in (44 mm) thickness of the leaf, then the 1/2 in (13 mm) stop on the far jamb, and you are left with 34 in (86 cm). That is the number that matters for moving furniture through the door, and it is 2 in less than the size printed on the invoice.

Standard leaf sizes in the United States#

Entry doors are quoted in feet and inches, and the nominal size is the real size. Height moves in two steps only: 80 in for almost everything, 96 in for tall openings on 9 ft ceilings and above.

The 42 in leaf is worth a caution. Weight rises with area, and a 42 x 96 in insulated slab can pass 200 lb (90 kg). At that point three hinges become four, and the frame wants to be reinforced rather than nailed to a trimmer stud.

The UK and European sizes, which are not conversions#

British external door sizes descend from imperial stock and were then converted, so the millimetre figures look arbitrary because they are. Nothing in the UK list is a rounding of anything in the US list.

Two near misses cause most of the trouble. A 2,032 mm leaf is exactly 80 in, so UK and US heights sometimes agree; a 1,981 mm leaf is 78 in and is 2 in short of every US frame. And 838 mm is 33 in, not 36 in, so an American door in a British opening leaves a 76 mm gap. The wider pattern of these mismatches is set out in door sizes by country, and the conversions themselves are in the unit converter.

Clear width, and the leaf size the code implies#

The IRC asks for one exit door with a clear width of 32 in (813 mm) and a clear height of 78 in (1,981 mm), measured with the leaf at 90 degrees. Work the subtraction backwards for each standard leaf, allowing 1.75 in for thickness and 1/2 in for the stop, and the list is short:

• 32 in leaf: 32.25 less 1.75 less 0.5 = 30 in clear. Fails.
• 34 in leaf: 34.25 less 1.75 less 0.5 = 32 in clear. Passes with nothing spare.
• 36 in leaf: 36.25 less 1.75 less 0.5 = 34 in clear. Passes.

So the smallest leaf that can legally be the required exit door is 34 in, and it has zero tolerance: a slightly thicker slab, a bulkier stop or a set of weatherseals eats the margin. This is the real reason the 36 in door is universal in American house building, and the reason a 32 in door on the front of a house is almost always a sign that the door is not the required exit. The general case for every opening in the house is in door sizes, swings and the space they need.

Sidelights, transoms and the head datum#

Glass beside and above the door is where the unit stops being a door and becomes a structural opening. The arithmetic is additive and it runs away fast.

A 36 in leaf with a 14 in sidelight each side gives 36 + 14 + 14 = 64 in of leaf and glass. Add two mullions at about 1.25 in and two outer jambs at the same, and the unit is roughly 69 in (1,753 mm) wide, needing a 71 in rough opening. That is nearly 6 ft of wall to be spanned, and the header sizing changes with it.

Transoms are a height problem instead. An 18 in transom over an 80 in leaf, plus about 2 in of head jamb and mullion, makes a 100 in (2,540 mm) unit. On a 96 in (8 ft) ceiling it simply does not fit. On a 108 in (9 ft) ceiling it leaves 8 in of wall above, which is tight but workable once the casing width is counted.

There is a proportion reason for transoms as well as a daylight one. Every interior door head in a normal house sits at 80 in, and that line runs through the whole plan; the same datum logic governs window head heights. A 96 in front door breaks the line unless every other door grows with it. A transom keeps the leaf at 80 in, holds the datum, and puts the extra height above it in glass.

Thickness, hardware and the one dimension that agrees#

Exterior leaves are 1.75 in in the US and 44 mm in the UK, and those two numbers differ by 0.45 mm. It is the only front door dimension the two systems share, and it is why mortice locks, cylinders, multipoint gearboxes and butt hinges are traded internationally while leaves are not. Interior doors sit at 1.375 in (35 mm) and are not suitable outside: the rebate is too shallow for a decent weatherseal, and the stile is too thin to take a mortice without losing stiffness.

Thickness also sets the hardware backset. A 44 mm leaf takes a 45 or 57 mm backset lock case in the UK, and a 2.375 or 2.75 in backset in the US. Handle and cylinder heights follow from there and are covered in door handle, lock and hinge heights.

Accessible entrances and where the numbers separate#

The 2010 ADA Standards ask for 32 in clear at 90 degrees, the same figure as the IRC, but they add manoeuvring space on both sides that a code-minimum house door rarely has. Approved Document M asks for 775 mm clear and a level threshold with an upstand no greater than 15 mm. The practical translation for a private house is to fit a 36 in or 900 mm leaf, use offset or swing-clear hinges if you need a few more millimetres, and treat the threshold as part of the door rather than part of the floor. The approach zone itself is a separate calculation, set out in accessible door widths, hardware and approach and in entry door clearances, landings and the approach.

Where the two systems genuinely disagree, and where each figure was published, is tracked in the standards and codes reference.