Roof Pitch Calculator

Calculate roof pitch by entering the rise and run or the angle in degrees. Learn more about measuring roof pitch and the rise and run below.

How to Calculate Roof Pitch

All homes and buildings have roofs. They may range from flat to very steep, some may have curves, and others may have multiple peaks and valleys. All of these roofs have one thing in common; however, they all have what is known as a pitch. Roof pitch describes the slope, or angle, of the roof.

Even flat roofs have a pitch, albeit a small one, as that slope is required to prevent rain and snow from gathering.

Knowing a roof’s pitch is essential in determining what type of material should be installed on the roof, the appropriate installation method, and how much roofing material you’ll need. It’s also an important factor in cold climates for calculating snow load.

Roof pitch, or slope, is a measure of vertical rise to horizontal run expressed in inches per foot, which is referred to as rise over run.^[1] Meaning that the roof is measured 12″ in from the edge in a horizontal line, then measured from this point straight up to where the roof intersects. A roof that rises 6″ vertically for every 12″ horizontally has a 6″ per foot, or a 6 in 12 pitch.

Thus, the pitch is the ratio of the rise in inches to a 12-inch run and is often expressed using a semicolon, for example, 6:12. Sometimes, the pitch is also expressed in fraction form using a fraction with a slash, such as 6/12.

You can measure roof pitch by finding the rise and run or by converting from the angle if it is known. See the chart below for the rise and run values for standard roof pitches.

We’ll cover four methods to calculate roof pitch below.

Method One: Measure From the Roof

Method Two: Measure From the Attic

Method Three: Measure the Total Rise and Run

Since the pitch is the rise over a 12-inch run, you can divide the run by 12 to get the multiplier; in this case, 120 ÷ 12 = 10.

Then, divide the rise by the multiplier to get the pitch, e.g. 48 ÷ 10 = 4.8. The pitch of this roof is 4.8:12. The calculator above can handle much of this math.

Method Four: Measure With a Speed Square

How to Convert Angle in Degrees to Roof Pitch

If you know the roof’s angle in degrees, you can find the roof pitch by converting the angle in degrees to a slope, then finding the rise by multiplying the slope by 12.

First, find the slope by finding the tangent of the degrees, e.g. slope = tan(degrees). Then multiply the slope by 12 to get the rise. You can then express the pitch as inches per foot.

How to Convert Roof Pitch to Degrees

To find the angle of a roof in degrees, convert the pitch to a slope, then convert to degrees by finding the slope’s inverse tangent, or arctangent. First, convert the pitch to a slope.

To do this, simply convert the rise and run as a fraction to a decimal form, e.g. rise/run = rise ÷ run = slope. For a pitch expressed in inches per foot, convert to a fraction first, e.g. a 4 in 12 pitch becomes 4/12, then divide.

Next, find the degrees by finding the slope’s inverse tangent, e.g. degrees = arctan(slope).

Standard Roof Pitches

Most roofs have a pitch in the 4:12 to 9:12 range. A pitch over 9:12 is considered a steep-slope roof, between 2:12 and 4:12 is a low-slope roof, and less than 2:12 is a flat roof.^[3]

The table below shows standard roof pitches and the equivalent grade and angle in degrees and radians for each.

Table showing standard roof pitches and the equivalent grade and angle in degrees and radians.

Pitch	Grade (slope)	Degrees	Radians
1/8:12	1%	0.6°	0.01
1/4:12	2.1%	1.2°	0.02
1/2:12	4.2%	2.4°	0.04
1:12	8.3%	4.8°	0.1
2:12	16.7%	9.5°	0.2
3:12	25%	14°	0.2
4:12	33.3%	18.4°	0.3
5:12	41.7%	22.6°	0.4
6:12	50%	26.6°	0.5
7:12	58.3%	30.3°	0.5
8:12	66.7%	33.7°	0.6
9:12	75%	36.9°	0.6
10:12	83.3%	39.8°	0.7
11:12	91.7%	42.5°	0.7
12:12	100%	45°	0.8
13:12	108.3%	47.3°	0.8
14:12	116.7%	49.4°	0.9
15:12	125%	51.3°	0.9
16:12	133.3%	53.1°	0.9
17:12	141.7%	54.8°	1
18:12	150%	56.3°	1
19:12	158.3%	57.7°	1
20:12	166.7%	59°	1
21:12	175%	60.3°	1.1
22:12	183.3%	61.4°	1.1
23:12	191.7%	62.4°	1.1
24:12	200%	63.4°	1.1

How Pitch Affects the Cost of Roofing

The pitch of a roof will have a definite impact on the cost to install or replace it. Steeper roofs cost more to install, so bear that in mind when choosing the right pitch for your project.

A low-slope roof might cost 10% more to install than a flat roof, while a steep-slope roof might cost 20-30% more. Roofs with a very steep pitch might cost even more than that to install.

Pitch Variations and Unusual Roofs

Not every roof is going to have a perfect, easy-to-measure angle. Some homes may have two different pitches for the roof.

For example, a dual-pitch gable roof has a different pitch on each side of the home. Gambrel and Mansard roofs are considered dual-angle roofs. The lower part of the roof is actually an extension of your home’s walls. This pitch is not quite vertical, but it is close.

In addition, some Mansard roofs are concave on this lower section, which can make it seem to have a different pitch. Both sections need to have their pitch calculated separately. If the roof is concave, you will need to measure from the interior if possible, as the way the roof curves outward at the bottom will give it the illusion of a less steep pitch than it truly has.

Most Gambrel and Mansard roofs are 20/12 on the front section, with a more standard 7/12 on the upper portion.

In complex roofs, such as cross gables, which may have multiple roof areas, you may need to check the pitch of each one – never assume that each section has the same pitch, as it is common for them to vary.

If you’re considering a new roof, we suggest getting several estimates to learn more about the right pitch for your roof and understand the cost of installation. We also cover more about roof replacement costs in detail in our cost guide.

Frequently Asked Questions

What is the standard roof pitch?

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What angle is a 4/12 roof pitch?