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. View the source
About this tool
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.
How roof pitch is worked out
Pitch is the rise of the roof for every 12 units of horizontal run. The angle in degrees is arctan(pitch ÷ 12), and the percent grade is pitch ÷ 12 × 100. Everything else on this page follows from that one angle.
Worked example: a 6/12 roof
- Angle: arctan(6 ÷ 12) = 26.57°, and the grade is 50%.
- Common rafter factor: √(1 + (6 ÷ 12)²) = 1.118. A rafter over a 12 ft run has a line length of 12 × 1.118 ≈ 13.42 ft, before the ridge deduction and the overhang.
- Hip or valley factor: √(2 + (6 ÷ 12)²) = 1.500, because a regular hip runs diagonally across the corner, 1.414 times as far as the common run.
- Roof area: the footprint, including the overhangs, multiplied by the same rafter factor.
Mistakes to avoid
- Using the full span as the run. On a simple gable, the run of each rafter is half the building’s width, measured level.
- Mixing up pitch and slope. Some plans give a slope as a fraction of the total span rather than rise per 12 of run. Check which one your drawings use.
- Treating the code minimum as a recommendation. The covering table lists the lowest pitch each roofing material is allowed on under the 2021 International Residential Code, a US code. Manufacturers’ instructions and the code adopted where you build come first, and outside the US other rules apply.
To find the pitch of an existing roof without climbing onto it, measure a rafter with the inclinometer set to pitch, or a photo of the gable end with photo measurement.
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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