Door Size Calculator

Work out door size instantly with clear inputs, formula shown and shareable results.

About Door Size Calculator

Door leaf size is the structural opening minus the frame on each side and a fitting clearance. The figure that matters for access is the clear opening with the door open at 90 degrees, which is smaller again by the door thickness and hinge projection.

Formula

Door sizing

leaf width = opening - 2 x frame - 2 x clearance; clear opening = leaf width - door thickness allowance

Worked example

With the default values below, Door Size Calculator returns Door leaf width of 834. Change any input above and every figure here is recalculated in your browser.

Inputs used

Structural opening width: 900 mm
Structural opening height: 2,050 mm
Frame thickness: 30 mm
Fitting clearance: 3 mm

Results

Door leaf width: 834 mm
Door leaf height: 2,007 mm
Clear opening width: 809 mm
Accessibility assessment: Meets the 800 mm accessible clear width

Step by step

1Values used
2Door sizing
3Door leaf width= 834 mm
4Door leaf height= 2,007 mm
5Clear opening width= 809 mm
6Accessibility assessment= Meets the 800 mm accessible clear width

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What clear width is needed for a wheelchair?

800 mm is the usual new-build requirement, with 750 mm accepted in existing buildings. A 900 mm structural opening only just achieves it.

Why subtract 10 mm at the head?

To allow for floor covering thickness and to leave a threshold gap so the door does not bind on carpet.