Roof Pitch to Degrees Chart

Roof pitch is written as inches of rise per 12 inches of run, but plans, tools and inclinometer apps often give the angle in degrees instead. The charts below convert every pitch from 1/12 to 24/12, and the common angles back to pitch. For an exact conversion from your own rise and run in any unit, use the roof pitch calculator.

Roof pitch chart: 1/12 to 24/12

Degrees are rounded to two decimals, grade to one, and the pitch multiplier (also called the slope factor) to three. Rise per foot is the vertical climb for every 12 in of horizontal run.

Degrees to pitch chart

Round-number angles rarely land on whole-number pitches. A 45° roof is exactly 12/12, but a 30° roof sits between 6/12 and 7/12, so builders usually round to the nearest whole rise.

Flat roof falls in mm per metre

In the UK, Ireland and Australia, flat and low-slope roofs are usually specified as a ratio of fall to length rather than a pitch. A 1:60 fall drops 1 mm for every 60 mm of run.

BS 6229:2018, Flat roofs with continuously supported flexible waterproof coverings — code of practice recommends a design fall of 1:40 so the finished roof still achieves at least 1:80 once construction tolerances and deflection are allowed for.

The formulas

Every value above comes from right-angle trigonometry, with rise and run in one unit:

• Angle = arctan(rise ÷ 12)
• Rise per 12 = 12 × tan(angle)
• Percent grade = rise ÷ 12 × 100
• Pitch multiplier = √(12² + rise²) ÷ 12, which equals 1 ÷ cos(angle)
• Fall of 1:n in mm per metre = 1000 ÷ n

Multiply a roof's horizontal footprint by the multiplier to get the sloped surface area, and multiply a horizontal run by it to get the length along the slope.

Minimum pitch by roofing material

The US International Residential Code sets a minimum slope for each roof covering. Check the manufacturer's installation instructions as well; they can require a steeper minimum.

International Code Council, 2021 International Residential Code, Chapter 9: Roof Assemblies — a porch or lean-to roof follows the same rules: its minimum pitch is set by the covering you put on it, not by the fact that it is a porch.

How to measure roof pitch

From inside the attic, hold a level horizontally against the underside of a rafter, mark 12 in along the level, and measure straight up from that mark to the rafter. That measurement in inches is your rise, so 7 in means a 7/12 pitch. From outside, you can rest one end of the level on the roof surface, hold it level, and measure down to the roof at the 12 in mark. An inclinometer or phone level app placed on a rafter gives the angle directly; the degrees table above converts it.

How precise does a phone reading need to be?

An inclinometer app reads to a tenth of a degree, but a reading taken on a real rafter is rarely that good. Near common roof pitches, one degree is worth roughly a quarter of an inch of rise per foot: 18.43° is 4/12, while 19.43° works out to about 4.23/12. At steeper pitches the gap widens, and one degree around 45° is closer to half an inch. Take three or four readings along different rafters, average them, and round to the nearest whole or half pitch in the chart. Framed roofs are usually built to whole or half pitches, so a reading of 26.2° is almost certainly a 6/12 roof (26.57°) with a little measurement error, not an unusual 5.9/12.

Planning a porch or shed roof from the height you have

For a new lean-to, porch or shed roof, the question often runs backwards: the height is fixed by a window, a door or a wall plate, and the pitch has to fit. Divide the drop you have by the horizontal distance the roof covers, in feet, to get the rise per foot. A porch roof 10 ft deep that can drop 24 in between the house wall and the beam gives 24 ÷ 10 = 2.4 in per foot, a 2.4/12 pitch, or about 11.3°. Then check that figure against the minimum-pitch table above. At 2.4/12, asphalt shingles are allowed but sit in the low-slope range that needs extra underlayment, while clay tile, wood shingles and slate are ruled out. If the pitch comes out below what your chosen covering allows, the choice is between a different covering, such as a membrane or standing-seam metal, and finding more height.

Pitch in other countries

The X/12 notation is used in the US and Canada. In the UK, Ireland, Australia and much of Europe, pitched roofs are normally specified in degrees, and tile and slate manufacturers publish their minimum pitch in degrees as well. The degrees-to-pitch chart above bridges the two: a product rated for 22.5° is about a 5/12 roof, and one rated for 12.5° sits between 2/12 and 3/12. Low-slope and flat roofs in those markets use the fall ratios in the flat-roof table instead.

A full example: from phone reading to pitch and roof area

Say a phone level laid on a rafter reads 33.7°. The degrees table shows 30° is 6.93/12 and 35° is 8.40/12, so the roof sits between them. Working it through: 12 × tan(33.7°) = 8.00, so the roof is an 8/12 pitch. The pitch chart gives its multiplier as 1.202. If the house footprint including overhangs is 1,500 sq ft, the sloped roof area is 1,500 × 1.202 = 1,803 sq ft. The angle alone would not have told you how much material to order; the multiplier is the number that carries through to the estimate. To turn that area into bundles, with waste for hips and valleys, enter the same footprint and pitch in the shingle calculator.

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