About the Door Size Calculator
Rough opening and structural opening sizes for a door, with the frame and clearances.
Also known as: door rough opening, door frame size, standard door sizes, door opening dimensions.
How to use this calculator
- Enter door leaf size, frame thickness, fitting gap each side, gap under the door and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
opening = leaf + fitting gaps + frame thickness both sides
Worked example
Using the values pre-filled in the calculator above:
- Door leaf size: 762 × 1981 mm (2'6")
- Frame thickness = 32 mm
- Fitting gap each side = 3 mm
- Gap under the door = 8 mm
the calculator returns:
- Structural opening: 842 × 2,034 mm
- Frame outside size: 832 × 2,024 mm
- Door leaf: 762 × 1,981 mm
- Leaf area: 1.51 m²