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- Roof pitch is the rise in inches for every 12 inches of horizontal run, written as 6/12.
- Angle = arctangent of rise ÷ run. A 6/12 pitch is about 26.57 degrees.
- Slope percent = rise ÷ run × 100, so a 6/12 roof has a 50% slope.
- The area multiplier turns a flat footprint into real roof surface area.
How to use the roof pitch calculator
Choose what you know
Pick rise and run, a pitch such as 6/12, or a roof angle in degrees.
Enter your numbers
For rise and run use the same unit for both, such as inches. For a pitch, enter the rise per 12 inches of run.
Add the building width
Enter the width of the building to estimate rafter length for a simple gable roof. Add an overhang in the advanced options if you have one.
Read the result
You get the pitch, angle, slope percent, area multiplier, roof type and rafter length, plus a chart of common pitches.
How roof pitch is calculated
Roof pitch compares how high the roof rises with how far it runs. Roofers use inches of rise for every 12 inches of run, because it is easy to measure with a level and a tape. The same triangle gives the angle, the slope percent and the length of the sloped surface.
Pitch, angle and slope
Pitch = rise ÷ run × 12 (written as pitch/12)
Angle = arctangent of (rise ÷ run)
Slope percent = rise ÷ run × 100
Area multiplier = √(1 + (rise ÷ run)²)
The area multiplier is the length of the sloped side divided by the length of the run.
Rafter length
Rafter length = (half the span + overhang) × area multiplier
This is the length along the slope for a simple gable roof, before ridge and cut details.
Worked examples
A 6/12 roof on a 24 ft wide building
Rise 6 and run 12 give a slope of 0.5. Half the span is 12 ft.
12 ft × 1.1180 = 13.42 ft along the slope.
An 8/12 roof with a 1 ft overhang
Rise 8 and run 12. Half the 24 ft span plus 1 ft overhang is 13 ft.
13 ft × 1.2019 = 15.62 ft.
From a 30 degree angle
The slope is the tangent of the angle: tan 30° = 0.5774.
A 30 degree roof is a little steeper than 6/12.
Roof pitch chart
Common roof pitches
Angle, slope percent and area multiplier.
Many guides call under 4/12 low slope, 4/12 to 9/12 conventional and over 9/12 steep.
Where a roof pitch calculator helps
Roofing estimates
Get the multiplier you need to turn floor area into roof area. Try the roofing calculator.
Choosing materials
Different roofing materials have minimum pitch limits, so check the manufacturer guidance.
Building and framing
Find rafter lengths and angles before cutting lumber.
Buying or inspecting a home
Understand how steep a roof is from a few measurements.
You can measure rise and run from the attic with a level and a tape, or work from building plans. Walking on a steep or wet roof is dangerous, so hire a professional if you are not sure. Results are estimates, and framing and roofing details should be checked against local building codes.
Roof pitch calculator FAQ
What is a 6/12 roof pitch?
It is a roof that rises 6 inches for every 12 inches of horizontal run. The angle is about 26.57 degrees and the slope is 50%.
How do I measure roof pitch?
Hold a level horizontally against the underside of a rafter, measure 12 inches along the level, then measure straight up or down to the rafter. That vertical distance is the rise per 12.
How do I convert pitch to degrees?
Divide the rise by 12, then take the arctangent. For 4/12, arctangent of 0.3333 is 18.43 degrees.
What is the area multiplier?
It is the factor that converts a flat footprint area into sloped roof area. A 6/12 roof has a multiplier of 1.118, so 1,000 square feet of footprint becomes about 1,118 square feet of roof.
What is a low slope roof?
A common definition is a pitch below 4/12. Some roofing materials need a minimum slope, so check the product instructions.
Is pitch the same as slope?
They describe the same steepness in different ways. Pitch is usually written as rise per 12, while slope can be given as a percent or an angle.