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Roof Slope Equivalents

(Three Ways to Express Roof Slope)

Roof Online Staff

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About Our Roof Slope Equivalents Table

The following table shows how the same common roof slopes can be expressed using rise-in-run ratios, 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 %

Formulas and Examples for Converting Roof Slopes

To make things easier, use a good calculator with all the 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.

Convert Standard Roof Pitch to Degrees

Rise-in-Run 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.

Convert Standard Roof Pitch to Percentage

Rise-in-Run 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.

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%

Convert Roof Slope in Degrees to Standard Roof Pitch

Degrees to Rise-in-Run: Find the tangent of the degree value. Multiply the tangent by the run (which is 12, since we’re doing this in inches). 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.

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°.

Convert Roof Slope in Percentage to Standard Roof Pitch

Percentage to Rise-in-Run: Divide the percentage number by 100. Multiply the result by the run (which is 12, since we’re doing this in inches). 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.