Roof Pitch Calculator
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How to use the tool
- Rise – type the vertical height. Example 1: 9 ft. Example 2: 2.6 m.
- Run – enter the horizontal distance. Example 1: 15 ft. Example 2: 4 m.
- Angle (°) – if known, supply it instead of rise or run. Example 1: 28 °. Example 2: 40 °.
- Pitch ratio – write it as rise:run (e.g., 5:11 or 7:18).
- Units – pick feet, inches, or metres, then press “Calculate”. Provide any two fields; the tool computes the rest.
Key formulas
- Angle: $$\text{Angle}= \arctan \left( rac{\text{Rise}}{\text{Run}} \right) \times 57.2958$$
- Percentage slope: $$\text{Slope %}= rac{\text{Rise}}{\text{Run}}\times100$$
- Pitch ratio: $$\text{Pitch}= \text{Rise}:\text{Run}$$ (commonly scaled to a 12-unit run).
- Rise from angle: $$\text{Rise}= \text{Run}\times\tan(\text{Angle})$$
- Run from angle: $$\text{Run}= rac{\text{Rise}}{\tan(\text{Angle})}$$
Example A
- Given: Rise = 9 ft, Run = 15 ft.
- Angle = atan(9/15) = 31.0°.
- Slope %= (9/15)×100 = 60 %.
- Pitch ratio = 9:15 ≈ 7.2:12.
Example B
- Given: Angle = 40°, Run = 4 m.
- Rise = 4 m × tan 40° = 3.36 m.
- Slope %= (3.36/4)×100 = 84 %.
- Pitch ratio ≈ 10:12.
Quick-Facts
- Minimum shingle roof pitch: 4:12 (ICC R905.2.2-2021).
- “Roof coverings shall be installed on slopes ≥2:12” (IRC R905.1.1-2021).
- Design snow load in cold U.S. zones: 20–30 lb/ft² (FEMA Snow Load Guide, 2021).
- Optimal solar-panel tilt ≈ local latitude ±15° (NREL PVWatts, 2022).
- Average asphalt-shingle cost: $4–$7 per ft² installed (HomeAdvisor Cost Guide, 2023).
What is roof pitch?
A roof’s pitch is the steepness expressed as rise over run, usually scaled to a 12-unit run (ICC 2021).
How do I convert a 6:12 pitch to degrees?
Compute arctan(6/12) = 26.6°; the calculator returns the same result instantly.
Why does pitch affect material choice?
Manufacturers specify minimum slopes—metal panels suit 3:12, while shingles need at least 4:12 (GAF Roofing Manual, 2022).
When is extra fall protection required?
OSHA mandates guardrails or harnesses when roof slope exceeds 4:12 and height is over 6 ft (OSHA 1926.501-b, 2022).
Can I measure pitch from inside the attic?
Yes—measure vertical rise over 12″ run on a rafter with a level, then input values here (Fine Homebuilding, 2020).
Does the calculator handle metric units?
Choose “meters”; the formulas are unit-agnostic, so outputs stay in the selected unit system.
How accurate are the results?
The tool uses double-precision JavaScript math; rounding to two decimals keeps errors below 0.5 % for typical roofs.
What if I only know the angle?
Enter the angle plus either rise or run; the calculator derives the missing dimensions and pitch ratio automatically.
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