Angle = arctan(rise ÷ 12). A 4/12 pitch is 18.43 degrees, 5/12 is 22.62 degrees, 6/12 is 26.57 degrees, 8/12 is 33.69 degrees and 12/12 is exactly 45 degrees.

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Roof pitch to degrees, every standard pitch

PitchAngleSlope %MultiplierHip / valleyRafter per 12" run
0.25/121.19°2.08%1.00021.414412.00"
0.5/122.39°4.17%1.00091.414812.01"
1/124.76°8.33%1.00351.416712.04"
1.5/127.13°12.50%1.00781.419712.09"
2/129.46°16.67%1.01381.424012.17"
2.5/1211.77°20.83%1.02151.429512.26"
3/1214.04°25.00%1.03081.436112.37"
3.5/1216.26°29.17%1.04171.444012.50"
4/1218.43°33.33%1.05411.453012.65"
4.5/1220.56°37.50%1.06801.463112.82"
5/1222.62°41.67%1.08331.474313.00"
5.5/1224.62°45.83%1.10001.486613.20"
6/1226.57°50.00%1.11801.500013.42"
6.5/1228.44°54.17%1.13731.514413.65"
7/1230.26°58.33%1.15771.529813.89"
7.5/1232.01°62.50%1.17921.546214.15"
8/1233.69°66.67%1.20191.563514.42"
8.5/1235.31°70.83%1.22551.581714.71"
9/1236.87°75.00%1.25001.600815.00"
9.5/1238.37°79.17%1.27541.620715.31"
10/1239.81°83.33%1.30171.641515.62"
11/1242.51°91.67%1.35661.685316.28"
12/1245.00°100.00%1.41421.732116.97"
13/1247.29°108.33%1.47431.781517.69"
14/1249.40°116.67%1.53661.833318.44"
15/1251.34°125.00%1.60081.887519.21"
16/1253.13°133.33%1.66671.943720.00"
18/1256.31°150.00%1.80282.061621.63"
20/1259.04°166.67%1.94372.185823.32"
24/1263.43°200.00%2.23612.449526.83"

Why would I need the angle instead of the pitch?

Saw bevels, angle finders, digital levels, CAD drawings and most non-US specification sheets all work in degrees, while carpenters and American roofing literature work in X/12. Converting between the two is the most common reason people reach for this tool.

What pitch is 45 degrees?

Exactly 12/12. The rise equals the run, so the angle is 45 degrees and the pitch multiplier is 1.414.

What is 30 degrees as a roof pitch?

About 6.93/12, which rounds to a 7/12 pitch. A 30 degree pitch is the standard for plain clay tiles in the UK.