Roof Area Pitch
Calculator
Results
- Slope factor
- 1.118033
- Roof surface area (m²)
- 134.164078
- Roof surface area (sq ft)
- 1,444.130123
Construction results
| Slope factor | 1.118033 |
| Roof surface area (m²) | 134.164078 |
| Roof surface area (sq ft) | 1,444.130123 |
formula-map diagram
- Slope factor
- 1.118033
- Roof surface area (m²)
- 134.164078
- Roof surface area (sq ft)
- 1,444.130123
Formula breakdown
Formula
A = footprint area × √(1 + (rise ÷ run)²)= 1.1180339887499
Note
Simplified model: results are quantity estimates only. They ignore openings, overlaps, cuts, site conditions and local building codes. Structural figures are not a substitute for a design by a qualified engineer.
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See all →Frequently asked questions
Why is a roof's surface area larger than the building's footprint?+
Because the roof is sloped, its actual surface spans a longer diagonal distance than the flat horizontal area it covers — the steeper the pitch, the more the true roof area exceeds the footprint, since the slope stretches the surface without changing the base dimensions.
What's the formula the calculator uses to find roof area from footprint and pitch?+
Roof area = footprint area × slope factor, where the slope factor is 1 ÷ cos(pitch angle) — as pitch angle increases toward vertical, the cosine shrinks toward zero and the slope factor grows, correctly reflecting that a steeper roof has proportionally more surface area.
How much more material does a steep roof need compared to a flat one, roughly?+
A common 6/12 pitch (about 26.57°) has a slope factor of roughly 1.118, meaning about 12% more material than the flat footprint suggests; a steeper 12/12 pitch (45°) has a slope factor of about 1.414, meaning over 40% more material — the increase accelerates noticeably at steeper pitches.
Should I measure the footprint from the outside walls or the roof overhang?+
Use the roof's actual horizontal extent, including eave overhangs, not just the building's wall footprint — overhangs are part of the roof surface that needs covering and are easy to forget if you measure only from the exterior wall line.
Why does the calculator need pitch as well as footprint, rather than just footprint and a rule-of-thumb waste factor?+
A generic waste factor doesn't account for the geometric reality that roof area scales precisely with the cosine of the pitch angle — two roofs with the same footprint but different pitches need genuinely different amounts of material, not just different amounts of waste allowance.