What this calculator does
Roof pitch describes how steep a roof is. This calculator converts rise and run into pitch, angle and slope multiplier.
Formula used
Pitch is rise per 12 units of run. Angle is arctangent of rise divided by run. Slope multiplier is rafter length divided by horizontal run.
How to read the result
The slope multiplier helps estimate sloped roof area from flat plan area, but real roofs need allowances for overhangs and details.
Assumptions
- Rise and run must use the same unit.
- Assumes a simple straight roof slope.
- Not a structural design tool.
Sources and checks
This calculator uses a standard public formula. Where rules or thresholds can change, source links are listed on the relevant page.
Frequently asked questions
What does 4 in 12 pitch mean?
It means the roof rises 4 units vertically for every 12 units of horizontal run.