Roof Pitch Calculator

Roof pitch is written as rise over run: how many inches the roof climbs for every 12 inches it travels horizontally. A 6/12 roof rises 6 inches per foot. That one number drives everything else, from the angle in degrees to the material you're allowed to put on it to how much bigger the roof surface is than the footprint underneath it.

How to measure roof pitch

You need a level (a 12 inch or 24 inch one is ideal) and a tape measure. The safest place to do it is inside the attic, against the underside of a rafter, where nobody has to get on the roof at all.

Hold the level horizontally against the rafter, with one end touching the underside.
Mark 12 inches along the level from that end.
Measure straight up or down from the 12 inch mark to the rafter.
That measurement in inches is your rise. Rise over 12 is the pitch.

If the rafter drops 7 inches over that 12 inch run, the roof is a 7/12 pitch. With a 24 inch level, measure at the 24 inch mark and halve the result.

From outside, you can do the same thing against a gable end, or hold the level out from the roof edge and measure down. A speed square with a pitch scale, or the level app on a phone laid against a rafter, gives you the angle in degrees instead, which the calculator converts.

Roof pitch chart

Pitch	Angle	Slope %	Pitch multiplier	Walkability
1/12	4.8 degrees	8.3%	1.003	Low slope, not shingle territory
2/12	9.5 degrees	16.7%	1.014	Minimum for asphalt shingles
3/12	14.0 degrees	25.0%	1.031	Easy walking
4/12	18.4 degrees	33.3%	1.054	Easy walking
5/12	22.6 degrees	41.7%	1.083	Comfortable
6/12	26.6 degrees	50.0%	1.118	The most common residential pitch
7/12	30.3 degrees	58.3%	1.158	Getting steep
8/12	33.7 degrees	66.7%	1.202	Steep, roof jacks needed
9/12	36.9 degrees	75.0%	1.250	Steep
10/12	39.8 degrees	83.3%	1.302	Steep
12/12	45.0 degrees	100.0%	1.414	Very steep

The angle comes from the arctangent of rise over run, and the multiplier is the square root of 1 plus (rise/run) squared. That multiplier is just the Pythagorean theorem applied to a slice of roof: the rafter is the hypotenuse of a triangle whose base is the run and whose height is the rise.

Turning pitch into roof area

The footprint of a house is not the area of its roof. A 6/12 roof covering a 40 by 28 foot footprint is not 1,120 square feet of roofing, it's 1,120 x 1.118, which is 1,252 square feet. The steeper the roof, the bigger the gap: at 12/12 the same footprint needs over 1,580 square feet of material.

Worked example. A simple gable roof on a 40 by 28 foot house at 6/12:

Footprint: 40 x 28 = 1,120 square feet
Roof surface: 1,120 x 1.118 = 1,252 square feet
Roofing squares: 12.5 (one square is 100 square feet)
With 10 percent waste: about 13.8 squares, so order 14
Shingle bundles at 3 per square: 42

For hips, valleys, dormers, and overhangs, the roof square footage calculator handles the whole ordering process including waste and bundle counts. This page is about the pitch itself.

The same multiplier works in reverse. If you know a roof's surface area and its pitch, divide by the multiplier to get the footprint, which is handy when you're checking a contractor's measurement against the house's dimensions.

What pitch means for materials

Pitch isn't just a math input. Building codes set a minimum slope for every roof covering, because water behaves differently on a shallow roof and wind-driven rain can push back up under the courses. These are the minimums under the residential code, summarized by section:

Material	Minimum slope	Code section
Asphalt shingles	2:12	R905.2.2
Clay and concrete tile	2.5:12	R905.3.2
Metal roof shingles	3:12	R905.4.2
Wood shingles and shakes	3:12	R905.7.2 and R905.8.2
Slate	4:12	R905.6.2
Mineral surfaced roll roofing	1:12	R905.5.2
Standing seam metal panels	0.25:12	R905.10.2
Built-up, modified bitumen, single ply	0.25:12	R905.9 to R905.15

Asphalt shingles carry an extra condition. Between 2:12 and 4:12 they need a doubled underlayment layer, which is why 4:12 is often quoted as the "normal" shingle minimum even though 2:12 is the code floor. Check the ICC code text and your local amendments before committing, since jurisdictions adopt different editions.

Safety and steepness

Anything up to about 4/12 feels like walking on a sidewalk. By 7/12 most people want roof jacks and planks, and above 8/12 the job needs proper fall protection and usually a professional. OSHA's construction rules require fall protection for work at six feet or more above a lower level, which covers essentially any roof on a house.

The practical version: if you're measuring pitch to plan a job, do it from the attic. If you're measuring to get a quote, take the number off the gable end from the ground with a level and a photo. Neither requires climbing.

Common mistakes

Measuring along the rafter instead of level. The run has to be horizontal. Hold the level bubble centered and measure vertically from the 12 inch mark, or the pitch comes out too shallow.

Calling it slope when it's pitch. In roofing, pitch usually means rise over a 12 inch run. In engineering, pitch sometimes means rise over the full span, which is half the number. If a figure looks half what you expect, this is why.

Using the footprint for the material order. The multiplier exists precisely because they differ. On a 6/12 roof you'd under-order by about 12 percent.

Averaging two different pitches. A house with a main roof at 6/12 and a porch at 3/12 has two roofs. Measure and calculate each separately, then add.

Forgetting the overhang. Roof area is measured to the edge of the eaves and rakes, not to the walls. A 12 inch overhang on all sides of a 40 by 28 house adds roughly 140 square feet of footprint before the multiplier.

Frequently asked questions

How do I calculate roof pitch?

Measure how many inches the roof rises over 12 inches of horizontal run. Hold a level against a rafter, mark 12 inches along it, and measure vertically to the rafter. A 6 inch rise over that 12 inch run is a 6/12 pitch.

What is a 6/12 roof pitch in degrees?

26.6 degrees. The angle is the arctangent of the rise divided by the run, so arctan(6/12) gives 26.57 degrees. As a percentage slope it's 50 percent.

What is the pitch multiplier and how do I use it?

It's the number that converts a flat footprint into actual roof surface. Multiply the footprint area by it: a 6/12 roof has a multiplier of 1.118, so a 1,120 square foot footprint becomes 1,252 square feet of roof. It equals the square root of 1 plus (rise/run) squared.

What is the most common roof pitch?

Most residential roofs fall between 4/12 and 9/12, with 6/12 the single most common in much of the US. It sheds water well, works with standard shingles, and is still walkable for maintenance.

What is the minimum pitch for shingles?

2:12 under the residential code, but shingles between 2:12 and 4:12 require doubled underlayment. Below 2:12 you need a low-slope system such as modified bitumen, TPO, or standing seam metal.

How do I measure roof pitch without getting on the roof?

Measure inside the attic against a rafter with a level and a tape. From outside, hold a level against the gable end and measure down 12 inches along it. Both give the same answer, and neither involves a ladder on the roof surface.

What's the difference between roof pitch and roof slope?

In practice they're used interchangeably in roofing, both meaning rise over a 12 inch run. Slope is sometimes expressed as a percentage instead, where a 6/12 roof is a 50 percent slope. The stricter geometric definition of pitch is rise over the total span, which halves the figure, so confirm which one a drawing means.

Roof Pitch Calculator