Roofing Calculator
Calculate roof area from pitch and footprint, plus tiles or sheets needed.
Please note: Material estimates for planning only. Always confirm quantities against your drawings, local building codes and supplier specifications before ordering. Structural work requires a qualified engineer.
What the Roofing Calculator does
A pitched roof covers more area than the building footprint beneath it. Dividing by the cosine of the pitch angle converts flat plan area into true sloped area, which is what you actually need to cover.
Formula
Pitch multiplier = 1 ÷ cos(Pitch angle)Pitch from ratio: angle = arctan(Rise ÷ Run)Roof area = (Length + 2 × Overhang) × (Width + 2 × Overhang) × Pitch multiplierUnits = ⌈Roof area × (1 + Waste %) ÷ Coverage per unit⌉
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Building length | number | Yes | Accepts more than 0. |
| Building length unit | one of 6 options | Yes | — |
| Building width | number | Yes | Accepts more than 0. |
| Building width unit | one of 6 options | Yes | — |
| Roof type | one of 3 options | Yes | — |
| Pitch given as | one of 2 options | Yes | — |
| Roof pitch | ° | In some modes | Accepts 0 or more, up to 85. Shown Pitch given as is Degrees. |
| Rise | number | In some modes | Accepts 0 or more. Shown Pitch given as is Rise per run (e.g. 6:12). |
| Run | number | In some modes | Accepts 1 or more. Shown Pitch given as is Rise per run (e.g. 6:12). |
| Eaves overhang | number | Yes | Accepts more than 0. |
| Eaves overhang unit | one of 5 options | Yes | — |
| Coverage per tile or sheet | m² | Yes | Accepts 0.001 or more. |
| Waste allowance | % | Yes | Extra material for cuts, breakage and offcuts. 5–10% is typical, more for complex layouts. |
| Price per tile or sheet | selected currency | Optional | Accepts 0 or more. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Building length unit and Building width unit.
- Enter Building length, Building width, Eaves overhang and Coverage per tile or sheet and 1 more.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Price per tile or sheet.
- Select Calculate.
Worked example
A 12 m × 8 m building, gable roof at 30°, 300 mm overhang, 0.2 m² per tile, 10% waste.
- Length
- 12 m
- Width
- 8 m
- Pitch
- 30°
- Overhang
- 300 mm
- Coverage
- 0.2
Footprint 12.6 × 8.6 = 108.36 m², multiplier 1.1547 → roof 125.13 m², +10% = 137.6 m² → 689 tiles.
Frequently asked questions
How do I convert a 6:12 pitch to degrees?
Take the arctangent of rise over run. A 6:12 pitch is arctan(0.5) = 26.57°, giving a 1.118 multiplier.
What is a roofing square?
A US unit equal to 100 square feet, or 9.29 m². Shingles are usually sold and quoted by the square.