Building & renovation
How do you calculate real roof area from floor plan and pitch?
Real roof area from footprint and pitch — optional membrane or tile pack estimate.
Quick answer
Roofing materials are ordered by real sloped area, not the house footprint on the plan. For a simple gable or shed roof, slope correction is footprint ÷ cos(pitch): a 30° pitch adds about 15% area versus flat projection. Complex hips, valleys and dormers need a site measure — this is a planning estimate for regular rectangles.
Advanced settings
Real roof area
88.3 m┬▓
For regular gable or shed roofs: real area = footprint ├À cos(pitch). Complex hips, valleys and dormers need a site measure ÔÇö this is a planning estimate only.
How it works
Optional material mode converts m² into pack counts using rough yields (membrane 1:1, tiles ~10 m²/pack, shingles ~3 m²/pack) — always verify with your supplier’s sheet size. Safety first on ladders and roofs; product links like roof waterproof membrane are for planning purchases, not installation shortcuts.
The square metres are only the first line of the order. The same area is needed again in underlay, the battens are bought in linear metres — roughly area divided by your batten spacing — and the ridge, hip, verge and eaves details are sold by the metre, not by the m², which is where two quotes for the same roof end up hundreds apart. Measure those runs while you are measuring the pitch. And order the spare tiles now rather than later: batches shade differently, and matching a run made five years ago is effectively impossible.
Frequently asked questions
How do I measure roof pitch?+
Use a smartphone inclinometer on the slope, or rise ÷ run: 3 m rise over 10 m run ≈ 16.7°. The calculator accepts common presets (15–45°) or a custom angle in the pitch field.
Footprint 8×10 m at 25° — what area?+
Footprint = 80 m². cos(25°) ≈ 0.906 → real area ≈ 80 ÷ 0.906 ≈ 88.3 m² before waste. Add 10% for cuts and overlaps on membrane or shingles.
Does this work for hip roofs?+
Not accurately — hips and valleys change true area versus a single rectangle. Use this for ballpark budgeting on simple roofs; order materials after a roofer’s measure or detailed plan for complex shapes.
Membrane vs tiles quantity — which to trust?+
Membrane is often sold by m² roll width — our 1:1 mode is close. Tiles and shingle packs vary wildly by profile and overlap; treat pack count as ±15% until you have the supplier datasheet.
As an Amazon Associate I earn from qualifying purchases — the price does not change for you.