01
Formula
Angle = arctan(rise ÷ run). Factor = hypotenuse ÷ run.
Percent slope is (rise ÷ run) × 100. A 6/12 pitch is a 50% slope and about 26.57 degrees. The factor is about 1.118, so the roof is about 11.8% larger than the footprint.
Apply for financingRoof pitch calculator
Roof pitch calculator for angle and slope factor
Enter the rise, the run, and the horizontal span. This roof pitch calculator returns the angle and the slope factor, and it is a rafter calculator for the common rafter on half of that span.
Roof angle
26.57degrees
Pitch6/12
Slope factor1.118
Percent slope50.0%
Common rafter8.94 ft
Planning estimate from the numbers you enter. Coverage, density, waste and price are assumptions, not a supplier quote or an engineering specification.
How it works
Pitch is rise divided by run.
A 6/12 pitch means 6 inches of rise for 12 inches of run. The angle is the arctangent of rise ÷ run, converted from radians to degrees. The slope factor is the rafter length per unit of run: the square root of (rise² + run²), divided by the run. Multiply the horizontal footprint by that factor to estimate the sloped area. The roofing calculator on this site does that multiplication for shingle squares.
02
Example
6 inches of rise on 12 inches of run.
The angle is 26.57 degrees. The pitch line reads 6/12. The slope factor is 1.118. On a 16 foot horizontal span, half the span is 8 feet, so the common rafter is about 8.94 feet along the slope, before overhang and cuts. Use the slope calculator when you want grade without a rafter.
03
Tips
Measure run horizontally.
Run is the level distance, not the distance along the shingles. Rise is vertical. A pitch written as 6/12 already assumes the run unit is 12. You can enter another run if you measured a different horizontal distance.
04
Equipment
Steep roofs are a lift conversation.
A boom lift or other roofing equipment can be part of an equipment financing request from $15,000 to $2 million. Dengaro is the broker. A participating provider decides the terms. This pitch result is not an offer.
Important questions
Know what to expect.
What is a slope factor?+
It is how much longer the roof surface is than the horizontal span. Multiply the footprint square footage by the factor to estimate the sloped area before waste.
Is 4/12 a different formula?+
No. Enter 4 and 12. The angle and the factor update. Lower pitches have factors closer to 1.
Does the roof pitch calculator include overhangs?+
Only if the rise and run you enter describe that part of the roof. Overhang area is extra square footage on the roofing calculator's footprint, not a change to the pitch.
Can I use this for a rafter length?+
For a single span, rafter length along the slope is run × slope factor, in the same units as the run. This page shows the factor. It does not subtract a ridge cut or add a tail.
Financing built into the sale