Door Calculator – Sizes & Rough Openings
Door planner: standard 0.8 × 2.0/0.9 × 2.1 m units, ADA 0.9 m clear, rough opening = unit + 5 cm width/+2.5 cm height for frames.
Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.
How does the doors calculator work?
A reliable doors takeoff follows one rule: measure twice, order once. The calculator converts your door size and pre-hung vs slab into dependable quantities using Rough Opening = Door + 5 cm W + 2.5 cm H (pre-hung frames), then adds the waste margin that experienced builders apply by default. Example: A 0.9 × 2.1 m pre-hung exterior door wants a 0.95 × 2.13 m opening with full-width flashing tape. Field tip: Exterior doors open inward in storms, outward in security planning - decide before framing. The result is broken down into purchasable units - bags, sheets, rolls or truck loads - so you can order the nearest whole unit without overbuying, and every figure traces back to the formula shown above.
- 1
Take dimensions
Note the door size and pre-hung vs slab for the area you are covering or filling.
- 2
Run the calculation
The calculator applies Rough Opening = Door + 5 cm W + 2.5 cm H (pre-hung frames) the moment you type.
- 3
Check the breakdown
Compare base quantity and waste-adjusted totals side by side.
- 4
Plan the purchase
Use the final figure to price and schedule the delivery.
Use Cases
Waterproofing wet areas
Membrane and corner counts for doors showers.
Siding replacements
Square counts for doors walls with 10% waste.
Energy audits
Document doors areas before and after upgrades.
Common Mistakes
Seams left untaped
Measuring the unit not the opening
Ignoring fire-rating requirements
FAQs
Standard interior door sizes?
Minimum clear width for wheelchair access?
How much bigger is a door rough opening?
How long to install a pre-hung door?
Measure that wall with more precision
A laser distance measure reads room and opening dimensions in seconds — the standard first step before area and door takeoffs.
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