Roof Area & Pitch Calculator — m, degrees, m²
How to use this calculator
Enter the building footprint plus a pitch angle, raw rise + run measurements in metres, or work back from a known slope. Pick gable, hip, or shed — the calculator returns pitch factor, actual sloped area in m², rafter length, ridge and hip lengths, and trim totals so material orders match what really gets installed.
Pitch factor (PF) = 1 / cos(angle). Multiply footprint area by PF to get true roof surface area.
Multi-section — Add additional roof sections with independent pitch for dormers or extensions.
Saved Calculations
| Time | Shape | Angle | PF | Footprint m² | Roof Area m² | Rafter m |
|---|
How to Calculate Roof Area from Pitch (Metric)
The footprint a roof covers in plan is always smaller than the sloped surface you actually clad. This metric tool multiplies footprint area by the pitch factor 1/cos(θ) to give the true roof area in m², plus rafter length, ridge and hip lengths, and the X:12 rise:run equivalent. Work from footprint and angle, or from field-measured rise and run in metres. Add extra sections for dormers and extensions.
How to use
Footprint + angle suits plans dimensioned by slope angle. Rise + run is for measured existing roofs. Always order cladding from the actual roof area, not the footprint — pass the result into the shingles m² & bundles calculator or the metal roofing panels calculator. For low-slope or flat sections use the flat roof membrane calculator, and size guttering with the gutter & downspout calculator.
Formulas
Pitch factor (PF) = 1 / cos(angle°). Rafter length = horizontal run × PF = run / cos(angle°). Rise = run × tan(angle°). Roof area = footprint area × PF (gable, hip, and shed all use footprint × PF for a uniform pitch). The rise:run output expresses the same slope in the common X:12 format. Add 10% waste for simple gables, 15% for hip and cut-up roofs.
Common angles
10° (low slope, PF 1.015) · 15° (minimum for many tiles, PF 1.035) · 20° (standard, PF 1.064) · 30° (steep, PF 1.155) · 45° (very steep, PF 1.414, 12:12 equivalent). For rafter timber volumes use the lumber volume calculator.
FAQ
Why is the roof area larger than the footprint? The roof follows the slope, so its true area is the plan footprint multiplied by the pitch factor 1/cos(θ) — at 30° that is about 15% more surface than the footprint.
Does a hip roof have a larger area than a gable? No. For the same footprint and uniform pitch the total surface is identical (footprint × PF); the hip simply splits the planes differently and adds hip rafters.
On install day
Three things estimators forget on a re-roof. Drip edge / eaves trim is mandatory at all eaves and rakes — order it in 3 m lengths and account for ~50 mm overlap per joint. Ridge tiles or capping are a separate line from the field tiles; mortar-bed or dry-fix systems differ by manufacturer. Concrete tile sits around €25–40/m² installed in 2025 EU pricing, clay €40–70/m², metal sheet €30–55/m², standing seam zinc €80–140/m². Waste — bump to 15% on hip and cut-up roofs and 20% with dormers; valleys, ridges and starter cuts eat material faster than the napkin math suggests. For tile counts feed the area-plus-waste value into the shingles m² & bundles calculator.
