Roof Pitch Calculator

Pick any point along a rafter or roof slope. Measure horizontally inwards (the run), then measure vertically from the end of that horizontal line up to the roof line (the rise). A spirit level and tape measure are all you need — a common approach is to hold the level out 1000 mm horizontally from the roof surface and measure straight down.

Use the same unit for both measurements and the calculator does the rest, converting your rise and run into degrees, a traditional pitch ratio and a percentage grade.

Pitch determines which roofing materials are suitable for your home. Tiles need enough fall to shed water reliably, while low-pitch roofs generally call for metal sheeting with sealed laps. Pitch also affects how much roof area you actually have — a steeper roof means more surface to cover. Once you know your pitch, try our roof area calculator to estimate your roof's true size.

If your roof's pitch seems borderline for its current material — or you're seeing leaks on a shallow section — it's worth having it looked at professionally.