Roof Pitch Calculator

Enter the rise and run of the roof, or its angle, to get the pitch, slope and rafter length.

I know the

Rise

Run

Angle (degrees)

Building width (span), optional

–

What roof pitch means

Pitch is how many units the roof rises for every 12 units of horizontal run. A 6/12 roof rises 6 inches per foot, an angle of 26.6°. Rise and run can be in any unit, as long as both use the same one.

Rafters

The rafter length factor is √(1 + (rise ÷ 12)²). Multiply it by half the building width (the run of one side) to get the rafter length from the wall to the ridge, before adding the overhang and allowing for the ridge board. With a 24 ft span at 6/12, each rafter is 12 × 1.118 = 13.4 ft, and the ridge is 6 ft above the wall plate.

Typical pitches

Under 2/12: flat or low-slope roofs that need a waterproof membrane, common for RCC roofs with a slight fall for drainage.
4/12 to 9/12: common for sheet and tile roofs.
Above 9/12: steep. These shed rain and snow well, but need more material and safety equipment.

Check the minimum pitch the manufacturer allows for your roofing sheets or tiles.

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How it works

Enter — type or paste your values or text.
Get the result — it is worked out in your browser.
Adjust — change the inputs to compare, or copy the result.

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