What this calculator does
Roof pitch & rafter length works out angle, slope factor and true roof area. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaPitch angle = atan(rise/run); rafter = √(rise²+run²); roof area = plan area × slope factor
The inputs explained
| Field | What to enter |
|---|---|
| Rise (m) | A number, measured in m. Starts at 2.4. |
| Run (half the span) (m) | A number, measured in m. Starts at 4. |
| Plan area of the roof (m²) | A number, measured in m². Starts at 120. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with rise
Every other input is held at the calculator’s starting values while rise varies. Select any row to load that scenario into the calculator.