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Roof Pitch Calculator

Pitch, Angle and Slope From Rise and Run

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How the Roof Pitch Calculator works

This roof pitch calculator converts a roof's rise and run into every way pitch is written: the x:12 pitch used in North America, the angle in degrees used in the UK and Europe, the percentage slope and a simple ratio. It also gives the sloping length for that rise and run and the area multiplier for working out roofing materials from a floor plan.

Rise is how far the roof climbs; run is the horizontal distance it climbs over, usually from the outside wall to the centre of the ridge. Because the ratio is what matters, you can use any unit as long as rise and run are the same, and a stepped measurement in feet and inches such as 4'6" works too.

How the roof pitch calculator works

The formula is angle = arctan(rise ÷ run), pitch = rise ÷ run × 12, and slope % = rise ÷ run × 100. The area multiplier is √(rise² + run²) ÷ run, which turns a flat plan area into the real sloping area. For example, a rise of 6 over a run of 12 is a 6:12 pitch, 26.6°, 50% slope and a multiplier of 1.118. A second example: 4 ft of rise over 10 ft of run is 4.8:12, 21.8° and 40%.

To measure an existing roof, hold a level horizontally against the underside of a rafter, mark 12 inches (or 1 m) along it, and measure straight up from that mark to the rafter; that is the rise per 12 of run. Phone apps and an angle finder on the roof surface also work.

Most roof coverings have a minimum pitch: concrete tiles often around 22.5°, slate around 20–25° and metal sheet as low as 5°. Check the manufacturer's figures to see how many degrees your chosen covering needs before you design or re-roof.

Common roof pitches as x:12, degrees, percentage slope and area multiplier

Pitch Degrees Slope Area multiplier
1:12 4.8° 8.3% 1.003
2:12 9.5° 16.7% 1.014
3:12 14.0° 25.0% 1.031
4:12 18.4° 33.3% 1.054
5:12 22.6° 41.7% 1.083
6:12 26.6° 50.0% 1.118
7:12 30.3° 58.3% 1.158
8:12 33.7° 66.7% 1.202
9:12 36.9° 75.0% 1.250
10:12 39.8° 83.3% 1.302
11:12 42.5° 91.7% 1.357
12:12 45.0° 100.0% 1.414
13:12 47.3° 108.3% 1.474
14:12 49.4° 116.7% 1.537
15:12 51.3° 125.0% 1.601
16:12 53.1° 133.3% 1.667
18:12 56.3° 150.0% 1.803
20:12 59.0° 166.7% 1.944
22:12 61.4° 183.3% 2.088
24:12 63.4° 200.0% 2.236

FAQ

What is a 6/12 roof pitch in degrees?

A 6/12 pitch rises 6 units for every 12 units of run, which is an angle of 26.57 degrees and a 50% slope. It is one of the most common pitches on houses in North America, steep enough to shed rain and snow but still walkable with care.

How do I convert roof pitch to degrees?

Divide the rise by the run, then take the arctangent. For a 4/12 pitch, 4 ÷ 12 = 0.333, and arctan(0.333) is 18.4 degrees. To go the other way, the rise per 12 is tan(angle) × 12, so 35 degrees is 8.4:12.

What is the minimum roof pitch?

It depends on the covering. Membrane roofs are called flat but still need a fall of about 1 in 40 (1.4°). Metal sheet can go down to about 5°, most concrete tiles to 12.5–22.5°, and plain clay tiles typically need 35° or more. Always follow the product's own data.

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