Door and Window Casing Calculator
Casing metres, pieces and board area from opening size and quantity.
Inputs
Result
Formula
| Perimeter | P = 2 × (width + height) |
| Total length | L = P × quantity |
| With waste | L = L × (1 + waste) |
| Pieces | n = ceil(L ÷ piece length) |
| Casing area | A = L × casing width |
Four 1.5 × 1.5 m windows with 60 mm casing, 2.4 m pieces and 8% waste: 6.00 m per opening, 24.00 m total, 25.92 m with waste, so 11 pieces and 1.44 m² of casing.
FAQ
Are door and window casings measured the same?
No. Doors are cased on three sides with nothing at the floor; windows need a sill board in addition, usually projecting 50-100 mm each side with returns. A window casing therefore uses more length and board than a door of the same size — do not price it at the door rate.
How is casing width chosen?
It must relate to skirting height and door proportions. The usual rule is casing equal to or slightly under the skirting: 60 mm casing with 80 mm skirting is commonest, 100 mm casing with 100-120 mm skirting. Too narrow looks flimsy; too wide crowds a small room and eats wall area.
Why do mitres crack?
Timber and MDF move with humidity; a mitre has a large contact area but the two pieces expand in different directions, so the joint opens. Better practice is a scribed or dowelled joint, proper wood glue rather than white glue, and sealing the end grain with finish promptly. Commercial work often uses square corner blocks instead.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.