What this calculator actually does
Roof pitch is a geometric slope. If rise and horizontal run use the same unit, their ratio determines pitch per 12, percent slope and the angle from horizontal. The slope factor is the hypotenuse ratio used to convert horizontal run into sloped length.
How to use this calculator
Measure or enter the vertical rise and horizontal run using the same unit.
Optionally enter a horizontal run length when you also need the sloped geometric length.
Review pitch per 12, angle, percent slope and factor as equivalent ways to express the same geometry.
Where people use it
- •Checking drawing or field slope measurements
- •Converting pitch notation to degrees
- •Early roofing geometry and sloped-length checks
Example: 6 rise over 12 run
6 ÷ 12 = 0.5, so the roof is 6:12, has a 50% slope and an angle of about 26.565°.
Assumptions and limits
- •This calculator describes geometry only. It does not approve a roof design, material, load path or construction method.
- •Field measurements can be affected by uneven surfaces and existing finishes; verify critical dimensions independently.
Frequently asked questions
What does a 6/12 roof pitch mean?+
The roof rises 6 units vertically for every 12 units of horizontal run.
How is roof angle calculated?+
The angle from horizontal is the arctangent of rise divided by run.
Is pitch the same as percent slope?+
They describe the same geometry differently. Pitch per 12 scales the rise to a 12-unit run, while percent slope multiplies rise/run by 100.
Semantic next steps
Continue the calculation
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