Roof Pitch Calculator
Enter the rise and the run, or the angle and the run, to get the pitch angle, the ratio, the gradient and the rafter length, with an optional overhang.
Worked examples
Rise and run
Rise 1,500 mm, run 3,000 mm, overhang 300 mm
Pitch angle: 26.6 degrees Rise: 1500 mm Run: 3000 mm Ratio: 1 in 2 (rise to run) Rise per 12 units of run: 6 in 12 Gradient: 50% Rafter length along the slope: 3354 mm Overhang along the slope: 335 mm Rafter length including overhang: 3690 mm Roof area factor: 1.118 times the flat area
The overhang is measured sideways, so it is longer along the slope.
Angle and run
Angle 35 degrees, run 3,000 mm
Pitch angle: 35 degrees Rise: 2101 mm Run: 3000 mm Ratio: 1 in 1.43 (rise to run) Rise per 12 units of run: 8.4 in 12 Gradient: 70% Rafter length along the slope: 3662 mm Roof area factor: 1.221 times the flat area
The rise is found from the angle and the run.
About Roof Pitch Calculator
This roof pitch calculator turns a rise and a run into the pitch angle, the ratio, the gradient and the length of the rafter. If you already know the angle you can enter that with the run instead and get the rise. It works in millimetres, centimetres, metres, inches or feet.
The run is the horizontal distance from the outside of the wall plate to a point under the ridge, which is half the span for a standard pitched roof. Add an overhang and the tool works out how much extra rafter that needs along the slope. Use the results for planning and check them with your roof designer.
How to use Roof Pitch Calculator
- Choose your units.
- Enter the rise and the run, or leave the rise empty and enter the angle.
- Add the overhang if there is one.
- Read the angle, ratio, gradient and rafter length.
Common uses
- Checking the pitch against the minimum for tiles or slates
- Ordering rafters for a shed, garage or extension
- Converting between an angle and a ratio
- Estimating the roof area from the flat area
Frequently asked questions
How do you work out roof pitch?
Divide the rise by the run to get the gradient, and take the inverse tangent of that to get the angle. A rise of 1,500 mm over a run of 3,000 mm is a gradient of 50% and an angle of about 26.6 degrees.
What does 6 in 12 mean?
It means the roof rises 6 units for every 12 units of horizontal run. It is the way pitch is often given on North American plans. 6 in 12 is about 26.6 degrees.
What is the run of a roof?
It is the horizontal distance covered by one side of the roof, from the wall to the point under the ridge. For a symmetrical roof it is half the span.
Does the rafter length include the overhang?
The main rafter length is to the wall plate line. If you enter an overhang, the tool shows it along the slope and the total length including it.