Roof Pitch to Angle Converter: Grade & Slope Factor

A roof slope can be written four ways, and this tool moves between all of them. Pitch is rise-in-12, the framing-square language a roofer uses. Angle is the same slope in degrees, the way a phone inclinometer or a protractor reads it. Grade is the percentage a highway sign shows. Slope factor is the multiplier that turns flat footprint area into true roof area.

They are all the same underlying ratio, so converting is pure trigonometry. Type a pitch and the angle is the arctangent of rise over 12; the grade is rise over 12 times 100; the slope factor is the square root of rise squared plus 144, divided by 12. Type an angle instead and the pitch is the tangent of that angle times 12. Type a grade and the pitch is the grade over 100 times 12. Whichever field you edit, the other three follow instantly.

This is the quick reference you reach for when a plan calls out a 30-degree roof and your framing square only speaks in twelfths, or when an app tells you the slope is 47 percent and you need to know whether standard shingles are rated for it. There is nothing to measure and nothing to order — it is a converter, so there is no diagram or print sheet, just the four equivalent numbers.