Roof Pitch Converter
Convert roof pitch between degrees, rise/run ratio, and percentage instantly. Enter any one value and get the others automatically. Free, no signup.
Rafter / Hip & Valley
Calculate rafter and hip/valley lengths from pitch and span
Plan-view distance from wall to ridge (one rafter)
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Pitch conversion — did you know?
Why three pitch formats exist
Degrees (UK/Europe — precise). Rise/run ratios (US — directly describes rafter geometry). Percentages (commercial flat roofing — 1:80 fall = 1.25%).
Degrees to ratio
Calculate tan(pitch°). At 35°, tan(35) = 0.700, ratio = 7:10. For Imperial 12-based: 0.700 × 12 = 8.4, so 8.4:12.
Ratio to degrees
arctan(rise ÷ run). For 9:12: arctan(0.75) = 36.87°. Most common conversion between UK and US specs.
Common pitch values
15° = 1:3.73 = 26.8% · 22.5° = 1:2.41 = 41.4% · 30° = 1:1.73 = 57.7% · 35° = 1:1.43 = 70% · 45° = 1:1.00 = 100%.
Formulas used
Degrees → ratio
ratio = tan(pitch°)
Ratio → degrees
pitch° = arctan(rise ÷ run)
Degrees → percentage
percent = tan(pitch°) × 100
Percentage → degrees
pitch° = arctan(percent ÷ 100)
Frequently asked questions
How do I convert degrees to a ratio?
Calculate tan(pitch°). At 35°, tan(35) = 0.700, ratio ~7:10 or 8.4:12 Imperial.
How do I convert 4:12 to degrees?
arctan(4/12) = 18.43°. A low-slope roof common in modern US construction.
What is 35 degrees as a ratio?
tan(35°) = 0.700, ratio ~1:1.43 or 8.4:12 in Imperial terms.
Is there a free roof pitch converter?
Yes — this converter is free, handles degrees/ratio/percentage, no signup required.