Roof Area Calculator
Calculate your roof area from ground floor dimensions and roof pitch. Get results in square feet, square meters, and roofing squares for accurate material estimates.
Roof Area Calculator
How to Calculate Roof Area
- Measure the ground floor footprint — the length and width of the building (or total floor area in square feet or m²).
- Determine the roof pitch — expressed as rise over 12 inches of run (e.g., 6/12 = 15 cm rise per 30 cm run).
- Calculate the pitch multiplier: √(1 + (pitch ÷ 12)²). The multiplier is dimensionless and applies identically in both systems.
- Multiply ground area by the pitch multiplier to get the actual roof surface area.
- Divide by 100 to convert sq ft to roofing squares (1 square = 100 sq ft ≈ 9.29 m²).
Imperial example: 1,200 sq ft floor, 6/12 pitch → 1,200 × 1.118 = 1,342 sq ft (13.42 squares).
Metric example: 111.5 m² floor, 6/12 pitch → 111.5 × 1.118 = 124.6 m² (≈ 13.42 squares).
Roof Pitch Multiplier Table
| Pitch | Multiplier | Area Increase |
|---|---|---|
| 0/12 (flat) | 1.000 | 0% |
| 1/12 | 1.003 | 0.3% |
| 2/12 | 1.014 | 1.4% |
| 3/12 | 1.031 | 3.1% |
| 4/12 | 1.054 | 5.4% |
| 5/12 | 1.083 | 8.3% |
| 6/12 | 1.118 | 11.8% |
| 7/12 | 1.158 | 15.8% |
| 8/12 | 1.202 | 20.2% |
| 9/12 | 1.250 | 25.0% |
| 10/12 | 1.302 | 30.2% |
| 11/12 | 1.357 | 35.7% |
| 12/12 (45°) | 1.414 | 41.4% |
Frequently Asked Questions
How do you calculate roof area from floor area?
Multiply the ground floor area by the pitch multiplier. The pitch multiplier equals √(1 + (pitch/12)²). For example, a 1,200 sq ft floor with a 6/12 pitch has a multiplier of 1.118, giving a roof area of about 1,342 sq ft.
Does roof pitch affect the total roof area?
Yes. A steeper pitch increases the roof area. A flat roof (0/12) has a multiplier of 1.000, meaning roof area equals floor area. A 12/12 pitch (45°) has a multiplier of 1.414, increasing the area by about 41%.
What is a roofing square?
A roofing square is a unit of measurement equal to 100 square feet. It is the standard unit used by roofing contractors to estimate materials. For example, a 2,000 sq ft roof equals 20 roofing squares.
Related Calculators
- Shingle Calculator — bundles, squares, and cost from roof area
- Roof Pitch Calculator — rise / run / angle from measurements
- Rafter Length Calculator — length, ridge height, run
- Paint Calculator — painting the surface area?
- 2D Area Calculator — area of complex roof geometries
- Area Unit Converter — convert between square feet, square meters, acres, hectares
- All Construction Calculators
Roof area calculations assume a simple gable or hip roof geometry. Complex roof shapes (dormers, valleys, multiple sections) may require additional measurements. Roofing squares equal roof area divided by 100. Always add 10–15% waste when ordering materials.
