Roofing calculator
Find the area of a roof of any kind — mono-pitch, gable, hip (four slopes), tent, half-hip or mansard — from the size of the house and the pitch, and how much covering, how many rafters, hips and battens it takes. The eaves and gable overhangs are counted apart, the roof is drawn from above, and the covering is rounded up to sheets, packs or pieces.
You need
1,177 pcs
112.02 m² of roof · 30° · covering + 5 %
- Rafters
- 40 rafters of 5.14 m
- Ridge
- 10.90 m
- Battens
- 16 rows · 325 m
- Trims
- eaves 21.8 m · gables 20.6 m
- Gable walls
- 18.48 m²
- Roof area: plan with overhangs ÷ cos 30°(10.90 × 8.90) ÷ 0.866 = 112.02 m²
- Covering + 5 %112.02 × 1.05 ÷ 0.1 → 1,177
- Rafters every 600 mm4.45 ÷ 0.866 = 5.14 m × 40
- Battens every 345 mm16 rows · 325 m
- Edges to trimeaves 21.8 m · gables 20.6 m
Consumption is the average from the «United Kingdom, Ireland, Australia and New Zealand» preset. Check it against your manufacturer's pack.
The calculator gives an estimate by the usual norms. Consumption depends on the product and the surface: check the manufacturer’s data before you buy.
How it’s calculated
- 1
Plan with overhangs = (length + 2 × overhang) × (width + 2 × overhang).
- 2
Roof area = plan area ÷ cos(pitch) — the same for mono-pitch, gable and hip roofs of one pitch.
- 3
Covering = roof area plus the allowance for the covering ÷ the useful area of one sheet, pack or piece, rounded up.
- 4
Rafter length = run ÷ cos(pitch); rafters along each slope at their spacing, plus one.
- 5
Battens run along the slope at their step: roof area ÷ step gives the running length.
Worked example
A gable roof over a 10 × 8 m house, 30° pitch, with the region’s usual overhang:
The input
- Roof
- Gable
- Length, m
- 10
- Width, m
- 8
- Pitch, °
- 30
- Eaves overhang, cm
- 45
- Gable overhang, cm
- 45
- Covering
- Concrete interlocking tiles (about 10 per m²)
The result
1,177 pcs
112.02 m² of roof · 30° · covering + 5 %
- Rafters: 40 rafters of 5.14 m
- Ridge: 10.90 m
- Battens: 16 rows · 325 m
- Trims: eaves 21.8 m · gables 20.6 m
- Gable walls: 18.48 m²
The calculation
- Roof area: plan with overhangs ÷ cos 30°(10.90 × 8.90) ÷ 0.866 = 112.02 m²
- Covering + 5 %112.02 × 1.05 ÷ 0.1 → 1,177
- Rafters every 600 mm4.45 ÷ 0.866 = 5.14 m × 40
- Battens every 345 mm16 rows · 325 m
- Edges to trimeaves 21.8 m · gables 20.6 m
How do I calculate the area of a roof?
Take the plan with the overhangs and divide by the cosine of the pitch. A 10 × 8 m house with 0.5 m overhangs is 11 × 9 = 99 m² in plan; at 30° the roof is 99 ÷ 0.866 = 114.3 m². At 15° the factor is 1.035, at 45° it is 1.414.
How much roofing material to buy?
Add the allowance of the covering — about 10–15 % for sheets and shingles, more for complex roofs with valleys and dormers — and divide by the useful area of one unit, not its full size: overlaps take part of every sheet.
Questions
Does a hip roof have more area than a gable one?
Not at the same pitch and overhangs: the area is the plan divided by the cosine of the pitch either way. A hip roof does need more cutting, so its allowance is usually higher.
What is the useful area of a sheet?
The part of it that covers the roof after the overlaps. It is on the product sheet; the calculator uses typical values of the region.
Can I enter the pitch as 6/12?
The site takes the pitch in degrees: 6/12 is 26.6°, 4/12 is 18.4°, 8/12 is 33.7°, 12/12 is 45°.
The same calculator in the Kvadrino app
Kvadrino for Android works offline: enter the room once and get tiles, paint, flooring and an estimate for the client. The app is in closed testing — write to us and we will add you as a tester.
Coming soon to Google Play