About the Roof Pitch Calculator
This roof pitch calculator converts between the ways roof steepness is described. Enter the rise and run you measured (for example 6 inches of rise over 12 inches of run) and it returns the pitch in the familiar x/12 format, the angle in degrees, the slope as a percentage and the pitch multiplier used to turn a flat footprint into true roof area. You can also start from an angle in degrees to find the pitch.
Roofers, framers and homeowners use it to choose suitable roofing materials, cut rafters, set a saw or speed square, and estimate materials. Many asphalt shingle products require a minimum slope, and steeper roofs usually need extra safety equipment.
Rise and run can be measured in any unit as long as both use the same one. A level held horizontally against the roof with a mark at 12 inches, and a tape measured straight down to the roof surface, gives the rise per 12.
How to use the roof pitch calculator
- 1Choose whether you know the rise and run, or the angle.
- 2Enter the rise and run in the same unit (or the angle in degrees).
- 3Read the pitch as x/12, plus the angle and slope percent.
- 4Use the pitch multiplier to convert footprint area into roof area.
Formula and method
Roof pitch expresses how many inches the roof rises for every 12 inches of horizontal run, so any rise/run measurement is scaled to a run of 12. The angle in degrees is the arctangent of rise ÷ run, and slope percent is rise ÷ run × 100.
The pitch multiplier is the length of the sloped surface per unit of horizontal run, from the Pythagorean theorem: √(1 + (rise/run)²). Multiplying a roof’s flat plan area by this factor gives the actual surface area to cover. Starting from an angle, the calculator uses rise/run = tan(angle).
- rise
- Vertical rise
- run
- Horizontal run in the same unit
- pitch
- Rise per 12 units of run
Worked examples
6 in rise over 12 in run
A 6/12 roof rises half as much as it runs, so the slope is 50% and the angle is arctan(0.5) = 26.57°. Its multiplier is √(1 + 0.25) = 1.118, so the roof surface is 11.8% larger than its footprint.
Low 4/12 ranch roof
A 4/12 pitch is a 33.3% slope, or 18.43°. The roof area is only about 5.4% larger than the footprint.
Measured 30 in rise over 48 in run
Scaling 30 over 48 to a run of 12 gives 30 × 12 ÷ 48 = 7.5, so the pitch is 7.5/12, an angle of about 32.0°.
45° roof angle
tan(45°) = 1, so the roof rises 12 inches for every 12 of run — a 12/12 pitch with a 100% slope and a multiplier of √2 ≈ 1.414.
Frequently asked questions
What is a 6/12 roof pitch in degrees?+
A 6/12 pitch is about 26.57 degrees, a 50% slope. It is one of the most common pitches for residential homes in North America.
How do I measure roof pitch?+
Hold a level horizontally against the roof or a rafter, mark 12 inches along it, and measure straight down from that mark to the roof surface. That vertical distance in inches is the rise per 12.
What is the minimum pitch for asphalt shingles?+
Asphalt shingles are generally installed on slopes of 2/12 or steeper, with special double underlayment required between 2/12 and 4/12. Always follow the shingle manufacturer’s instructions and local building code.
What is a pitch multiplier?+
It is the factor that converts flat (plan) area into sloped roof area: √(1 + (pitch/12)²). For a 6/12 roof it is 1.118, so a 1,000 sq ft footprint has about 1,118 sq ft of roof.
What is the difference between pitch and slope?+
They describe the same steepness. Pitch is usually written as rise per 12 inches of run (6/12), while slope may be given as a ratio, a percentage (50%) or an angle (26.6°).