Ways to Express Roof Slope: Pitch, Degrees, and Percentage

(Roof Slope Equivalents with Conversion Formulas)

Roof Online Staff

See More Roofing Topics

Table of Contents

Note: Correct Format for Stating a Standard Roof Pitch

When referring to a specific roof pitch in writing, the proper way to express the pitch is in the form “X-in-12”. If you’re talking about a roof that rises 4 units for every 12 units it runs horizontally, you would say that the roof has a “4 in 12 pitch”.

The accepted alternative to this, particularly in roofing industry literature, is to use a colon instead of the word “in”. This style takes the form “X:12” or “X : 12”, so for a 4 in 12 pitch, you would write “4:12 pitch”.

The use of a slash, as in 4/12, is not normally used by roofing professionals, even though you see it almost everywhere else. This is to avoid confusion: the slash normally means “divided by”, and that is not what you are trying to say when stating a roof pitch.

Ways to Express Roof Slope: About This Table

The following table shows how the same common roof slopes can be expressed using rise-in-run ratios (standard pitch), degrees, and percentages.

See below, after the table, for directions on how to convert any roof slope from one form to another. Even roof slopes not shown in the table. It’s just a little math.

Also see our page Roof Pitch to Degrees – Degrees to Roof Pitch which has conversion charts that convert slopes from 1 to 72 degrees into standard roof pitch (X-in-12) and roof pitches from ⅛-in-12 to 36½-in-12 into degrees.

If you’re not sure what the slope of your roof is and you want to determine that in either degrees or rise-in-run, we recommend this slope finder on Amazon. It’s very inexpensive and very accurate.

If you’re using this table, you might like to get yourself a construction calculator. This one is very good.

Table of Roof Slope Equivalent Expressions

Roof Slope
(Standard Roof Pitch)
Roof Slope
(Degrees)
Roof Slope
(Percentage)
0.25:12 1.193° 2.08 %
0.5:12 2.386° 4.17 %
1:12 4.76° 8.33 %
2:12 9.46° 16.67 %
3:12 14.04° 25 %
4:12 18.43° 33.33 %
5:12 22.62° 41.67 %
6:12 26.57° 50 %
7:12 30.26° 58.33 %
8:12 33.69° 66.67 %
9:12 36.87° 75 %
10:12 39.81° 83.33 %
11:12 42.51° 91.67 %
12:12 45° 100 %
13:12 47.29° 108.33 %
14:12 49.4° 116.67 %
15:12 51.34° 125 %
16:12 53.13° 133.33 %
17:12 54.78° 141.67 %
18:12 56.31° 150 %
19:12 57.72° 158.33 %
20:12 59.04° 166.67 %
21:12 60.26° 175 %
22:12 61.39° 183.33 %
23:12 62.45° 191.67 %
24:12 63.43° 200 %
25:12 64.36° 208.33 %
26:12 65.22° 216.67 %
27:12 66.04° 225 %
28:12 66.80° 233.33 %
29:12 67.52° 241.67 %
30:12 68.20° 250 %

Ways to Express Roof Slope: How to Convert from One to Another

To make things easier, use a good calculator that can perform the trigonometric functions.

There’s a good calculator here at web2.0calc.com.

Click the “2nd” button in the top left of the calculator field to find the “atan” (arctangent) button. Enter the number (0.54167 in the following example) and click the “atan” button and then the “=” button.

Formula: Convert Standard Roof Pitch to Degrees

Standard Roof Pitch to Degrees: Find the arctangent of (rise/run).

Example:

For a 6-1/2 inch in 12 inch slope (6-1/2 = 6.5),

arctan(6.5 divided by 12)

arctan(0.54167) = 28.44° slope.

Formula: Convert Standard Roof Pitch to Percentage

Standard Roof Pitch to Percentage: Divide the rise by the run and multiply by 100.

Example:

For a 3/8 inch in 12 inch slope (3/8 = 0.375),

0.375 divided by 12 = 0.03125

0.03125 x 100 = 3.125

3/8 in 12 slope = 3.125% slope.

Formula: Convert Roof Slope in Degrees to Percentage

Degrees to Percentage: Find the tangent of the degree value. Multiply by 100.

Example:

For a slope of 25°,

tan(25) = 0.4663

0.4663 x 100 = 46.63

25° slope = slope of 46.63%

Formula: Convert Roof Slope in Degrees to Standard Roof Pitch

Degrees to Standard Roof Pitch: Find the tangent of the degree value. Multiply the tangent by the run (which is always 12 in standard roof pitch). That gives you the rise. Put them together as rise-in-run.

Example:

For a slope of 35°,

tan(35) = 0.700

0.7 x 12 = 8.4

giving you a slope of 8.4-in-12 or

8-2/5 inches in 12.

Formula: Convert Roof Slope in Percentage to Degrees

Percentage to Degrees: Divide the percentage number by 100. Find the arctangent of the resulting value.

Example:

For a slope of 55%,

55 divided by 100 = 0.55

arctan(0.55) = 28.81

55% slope is equal to a slope of 28.81°.

Formula: Convert Roof Slope in Percentage to Standard Roof Pitch

Percentage to Standard Roof Pitch: Divide the percentage number by 100. Multiply the result by the run (which is always 12 in standard roof pitch). That gives you the rise. Put them together as rise-in-run.

Example:

For a slope of 25%,

25 divided by 100 = 0.25

0.25 x 12 = 3

giving you a slope of 3-in-12.