How do I calculate roof area from pitch?

Multiply plan area by the pitch factor 1/cos(pitch°). For example, plan area 60 m² at 35° gives 60 ÷ cos(35°) ≈ 73.3 m².

What measurements do I need?

Length and width of the building footprint, plus the roof pitch. For complex roofs, split into rectangles/triangles, calculate each, and add them up.

Does the roof shape change the calculation?

Yes. Gable and mono roofs are straightforward. Hip and pyramid roofs still use a pitch factor but need correct plan dimensions. Mansard roofs have two pitches per side and should be split into upper and lower slopes.

Should I add extra area for overlaps or detailing?

Yes. Add 5–10% for simple roofs and 10–15% for complex details, valleys, dormers, or heavy cutting.

Roof Area Calculator

Find true roof surface area from plan dimensions and pitch. Supports gable, hip, pyramid, mansard and mono-pitch.

1) Roof Shape

Select Roof Shape

Plan dimensions follow the footprint. Surface area adjusts for pitch. Mansard uses lower/upper pitch and run split.

2) Dimensions & Pitch

Units:

Length (m)

Width (m)

Pitch Angle (°) (single-slope shapes)

Or Known Roof Surface Area (m²)

Running Total:

Total Area 0.00 m²

Sections Added 0

Results

Plan Area — m²

Length × Width

Pitch Factor —

= 1 ÷ cos(pitch)

Surface Area — m²

Pitch-adjusted; mansard uses dual-slope model.

Notes —

Enter a known area to bypass pitch.

For complex roofs, calculate each section and add them with the totaliser.

Roof Area Calculator UK | Measure Roof Size by Pitch, Shape & Plans (2025)

Roof Area Calculator Guide (UK 2025)

The Roof Area Calculator helps you estimate roof surface area from simple measurements. Enter length, width, and pitch — or a known plan area — and choose between gable, hip, pyramid, mansard, or mono-pitch shapes.

How the Calculator Works

Plan Area = Length × Width Surface Area (simple roof) = Plan Area ÷ cos(pitch°) Mansard Roofs = (Lower run ÷ cos lower°) + (Upper run ÷ cos upper°)

For pitched roofs, the pitch factor increases the plan area to account for slope. Mansards combine two angles per side, which the calculator handles automatically.

Already have roof area from drawings? Enter it directly and skip pitch.

Supported Roof Shapes

Shape	Common Use	Notes
Gable	Most houses	Two slopes. Simple and accurate using pitch factor.
Hip	Detached homes	All four sides slope. Add ridge tiles separately.
Pyramid	Square buildings	Four equal slopes meeting at a single point.
Mansard	Townhouses / lofts	Steep lower + shallow upper slopes for space efficiency.
Mono-pitch	Lean-tos, extensions	Single slope; easy calculation.

For L-shaped or complex roofs, split into rectangles or triangles, run the calculator for each, and sum results.

Pitch Factors (Quick Reference)

Pitch (°)	cos(pitch)	Pitch Factor (÷cos)
15°	0.966	1.035
25°	0.906	1.104
30°	0.866	1.155
35°	0.819	1.221
40°	0.766	1.305
45°	0.707	1.414

Multiply your plan area by the pitch factor. Example: 80 m² at 35° → 80 × 1.221 = 97.7 m².

Example Roof Area Estimates

Roof	Dimensions	Pitch	Surface Area
Gable	10 × 6 m	35°	≈ 73.3 m²
Hip	12 × 7 m	30°	≈ 97.0 m²
Mono	8 × 4 m	30°	≈ 36.9 m²
Mansard	10 × 8 m (70° lower, 25° upper)	Split	≈ 105–120 m² (calculated precisely in tool)

Figures are approximate. Always confirm dimensions from plans or physical measurement.

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Frequently Asked Questions

How accurate is this roof area method?

For standard pitched roofs, it’s very accurate if your measurements and pitch are correct. Mansards and broken roofs should be split into multiple sections.

How do I find my roof pitch?

Use a smartphone inclinometer app or a simple pitch finder tool on a rafter. Enter the measured angle into the calculator.

Can I calculate in feet or yards?

Yes. The calculator supports both metric (m²) and imperial (ft²) units with automatic conversion.

Should I add extra area for detailing?

Always allow 5–15% extra for overlaps, valleys, dormers, and trimming. Larger or more complex roofs need higher allowances.

Note: Always cross-check with supplier and product data sheets before ordering tiles, membranes, or structural materials.

Roof Area Calculator

1) Roof Shape

2) Dimensions & Pitch

Mansard Parameters

Results

Roof Area Calculator Guide (UK 2025)

How the Calculator Works

Supported Roof Shapes

Pitch Factors (Quick Reference)

Example Roof Area Estimates

Affiliate Tools & Materials

Related Calculators

Frequently Asked Questions

How accurate is this roof area method?

How do I find my roof pitch?

Can I calculate in feet or yards?

Should I add extra area for detailing?

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