Roof pitch calculator
Pitch, degrees, rafters and roof area
Type 6, 6:12 or 6 1/2.
Result
Your answer appears here as you type.
Rafter length
Use any length unit, the same for all three. Fractions like 3/4 work too.
Roof area
Exact for any roof whose planes share one pitch — gables, hips and valleys alike.
Minimum pitch by roof covering
Built-up roofing
Minimum 1/4:12 · R905.9.1
Mineral-surfaced roll roofing
Minimum 1:12 · R905.5.2
Asphalt shingles
Minimum 2:12 · R905.2.2
Clay or concrete tile
Minimum 2 1/2:12 · R905.3.2
Metal roof shingles
Minimum 3:12 · R905.4.2
Wood shingles
Minimum 3:12 · R905.7.2
Wood shakes
Minimum 3:12 · R905.8.2
Slate
Minimum 4:12 · R905.6.2
Code minimums from the 2021 International Residential Code, section R905. Manufacturer instructions and the code adopted where you build take precedence.
Roof pitch calculator
Convert a roof pitch between x:12, degrees and percent, and get rafter and hip factors, cut angles, rafter length and roof area — with the minimum pitch for each roof covering from the International Residential Code.
Frequently asked questions
How do you calculate roof pitch?
Roof pitch is how many units the roof rises for every 12 units of horizontal run, written as 4/12 or 4:12. Divide the rise by the run and multiply by 12: a roof that rises 3 feet over a run of 9 feet has a pitch of 4/12.
To measure it, rest one end of a level on the roof, hold the level horizontal, and measure straight down from its 12-inch mark to the roof surface: that measurement in inches is the pitch. The angle in degrees is the arctangent of rise ÷ run, and the calculator on this page converts between pitch, degrees and percent.
What is a 4/12 roof pitch in degrees?
A 4/12 roof pitch is 18.43°. The roof rises 4 inches for every 12 inches of horizontal run, a grade of 33.3%, which counts as a low-to-moderate slope.
Under the International Residential Code, 4/12 is the lowest pitch where asphalt shingles need no extra underlayment, and the minimum pitch for slate. Open 4/12 in the calculator for its rafter factors, cut angles and roof area.
How can I find my roof pitch without going on the roof?
Measure it from the attic or from the ground. In the attic, lay your phone along the top edge of a rafter and open the inclinometer: set its units to roof pitch and it reads the pitch directly.
From the ground, photograph the gable end from straight in front and open the picture in photo measurement. Measure the angle between the sloping edge of the roof and a horizontal line such as the eaves, then enter that angle in degrees here to get the pitch.
Guides
About these measurements
Readings are estimates taken from rendered pixels and consumer device sensors. Do not rely on them for structural engineering, surveying, manufacturing inspection, navigation, or medical decisions. Check anything safety-critical with a calibrated instrument.
All processing happens in your browser. No image, camera frame or sensor reading is ever uploaded.
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