Roof Pitch Calculator

Roof pitch is the number of inches a roof rises for every 12 inches it runs level, written as a ratio such as 6/12. Slide the calculator to your rise and it shows the angle in degrees and the area factor that turns a flat footprint into true roof surface; a 6/12 roof, for example, sits at about 26.6 degrees with a factor of 1.118.

Roof pitch chart: angle and area factor for each pitch

Pitch, angle and area factor are three ways of describing one slope. At the shallow end, 1/12 is about 4.8 degrees with a factor of 1.003, 2/12 is 9.5 degrees and 1.014, and 3/12 is 14.0 degrees and 1.031. Roofs this flat add almost no surface over their footprint.

The everyday range for shingle roofs starts at 4/12, which is 18.4 degrees and 1.054. From there, 5/12 is 22.6 and 1.083, 6/12 is 26.6 and 1.118, 7/12 is 30.3 and 1.158, 8/12 is 33.7 and 1.202, and 9/12 is 36.9 and 1.250.

Steep roofs climb fast. A 10/12 roof is 39.8 degrees with a factor of 1.302, 11/12 is 42.5 and 1.357, and 12/12 is exactly 45 degrees and 1.414. At the top of the slider, 18/12 is 56.3 degrees and 1.803.

Notice how the factor grows. Going from 2/12 to 4/12 adds about four square feet of roof for every hundred of footprint, while going from 10/12 to 12/12 adds more than eleven. A one-inch mistake in the rise matters far more on a steep roof.

What roof pitch means: rise, run, slope and angle

The first number in a pitch is the rise and the second is the run, and the run is almost always 12 because framers work in inches. A 7/12 roof gains 7 inches of height for every foot you move in from the outside wall toward the ridge, and you may hear it called a 7 pitch or 7 in 12.

Older carpenters sometimes use pitch for something else: the rise divided by the whole span of the building, wall to wall. In that language a quarter pitch is the same roof as 6/12, a third pitch is 8/12 and a half pitch is 12/12. Convert a fraction like that before you use the calculator.

On house plans, pitch appears as a small right triangle beside the roof line, with 12 on the flat leg and the rise on the upright one. The angle in degrees is the arctangent of the rise divided by 12, which the calculator works out for you. Degrees suit phone level apps and saw settings, while the ratio is what roofers, codes and shingle wrappers use.

How to measure roof pitch without climbing on the roof

Start with paper. Building plans, truss drawings and permit sets usually mark the pitch with that little triangle. If the house has an unfinished attic, the rafter method in the roof cost guide works from inside with a level and a tape.

From outside, a photo does surprisingly well. Walk back from a gable end until you can see the whole triangle, stand square to the wall rather than off to one side, and zoom in instead of stepping closer so the camera isn't tilted up. Then lay a protractor or an angle-measuring app over the photo along the rake trim and read the degrees. Match the angle to the chart above, and take two or three photos from different spots to check yourself.

On a hip roof with no gable, photograph a dormer end, a garage gable, or the slope seen from the side against the sky. Shadows, gutters and a sagging ridge can throw a reading off by an inch of rise, so treat a photo measurement as close, not exact.

Measuring roof pitch safely: ladders, roofs and weather

Finding the pitch never requires walking the roof, and for a homeowner it shouldn't. Shingles that look dry can carry dew or frost, loose granules roll underfoot, and a slope that feels gentle from the ladder gets steeper with every step. Roofers on anything past a moderate pitch wear harnesses tied to anchors, which says a lot about how quickly things go wrong up there.

If you do use a ladder at the gable end, keep its feet on solid, flat ground and angle it so the distance from the wall is about a quarter of the height it reaches. Let it extend about three feet past the edge, keep three points of contact, and carry tools in a pouch. Have someone hold the ladder, and look up for power lines before raising it, especially an aluminum one.

Skip the job in wind, rain or cold. A reading from the ground, from plans or from the attic is accurate enough for the calculator, and any roofer quoting your roof will measure the pitch again anyway.

4/12, 6/12, 8/12 and 12/12 roof pitch compared

A 4/12 roof is the low end of the normal range and is common on ranch houses and wide single-story homes. Crews walk it comfortably, shingles on it need only a single layer of underlayment, and the attic underneath is low.

A 6/12 roof sits in the middle and turns up on a great many American houses. It is still walkable for a crew in dry weather, sheds snow better than 4/12 and gives the attic more headroom. Around 8/12 the picture changes. Footing gets uncertain, crews set roof jacks and harnesses, and many roofers begin adding a steep charge.

A 12/12 roof is a 45 degree slope, found on Cape Cods, A-frames, Tudors and many older two-story homes. Crews work it from staging boards and ropes. It carries about four tenths more surface than its footprint, so it takes noticeably more shingles and labor per foot of house, but it sheds rain and snow quickly and can hold a whole room inside.

Limits of a roof pitch calculator

The math in the calculator is exact; the inputs never are. Many houses mix pitches, with a steep main roof, a shallower porch and a nearly flat addition, and each section needs its own reading. One pitch applied to the whole house can be off by several squares.

The area factor holds for any roof whose slopes all share one pitch, gable or hip, because each plane gains the same proportion of surface over its footprint. It does not account for dormers, which add cheek walls and small roofs of their own, for a sagging ridge, or for overhangs left out of the footprint.

The last line of the calculator puts your pitch in context. Under 2/12 is membrane territory, 2/12 to just under 4/12 is low slope where shingles need extra underlayment, 4/12 through 9/12 is the usual shingle range, and anything steeper is harder to walk and often priced higher. The shingle maker's instructions and your local code have the final say, and a roofer's own measurement settles the order.

Questions people ask

What is the most common roof pitch?

There is no single standard, but most sloped house roofs in the United States fall between 4/12 and 9/12. The middle of that range is very common because it sheds water and snow well and is still workable for a crew.

How do you convert roof pitch to degrees?

Divide the rise by 12 and take the arctangent of the result. For a 6/12 roof, 6 divided by 12 is 0.5, and the arctangent of 0.5 is about 26.6 degrees. To go the other way, take the tangent of the angle and multiply it by 12 to get the rise.

Is a 4/12 roof pitch too low for shingles?

No. Asphalt shingles are made for 4/12 and steeper with an ordinary single layer of underlayment. They can go down to 2/12, but between 2/12 and 4/12 the shingle maker and the code call for extra protection underneath.

What roof pitch is considered steep?

For walking and pricing, many roofers treat somewhere around 7/12 to 9/12 as the point where a roof turns steep, because crews need roof jacks, harnesses and more time per square. Above 12/12, most crews work entirely from staging and ropes.

How can I find my roof pitch without getting on the roof?

Check the house plans or truss drawings for the pitch triangle, measure a rafter from inside the attic, or photograph a gable end straight on and measure the angle of its rake trim with a protractor app.

Read: Estimates and Squares: How Many Shingles Will I Need?

Read: How Much Does A New Roof Cost?

Read: Shingle Roofs