Roof pitch, angle and slope, rafter length, roof area and squares of shingles
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Roof pitch is the rise in inches for every 12 inches of run. A 6/12 roof rises 6 inches per foot, which is 26.57 degrees and a 50% slope. Its roof area is 1.118 times the footprint, so a 1,500 square foot footprint needs 16.8 squares of shingles before waste.
Under "I know the", pick Pitch, Angle or "Rise and run", and enter that measurement.
Enter the "Rafter run (half the span)" and the "Overhang, horizontal".
Enter the "Footprint with overhangs", the "Waste allowance" and the "Bundles per square".
Read the Pitch with its angle and percent slope, the "Rafter length" and the "Roof area", then press Share result.
Roofers, framers and building codes describe a roof's steepness in three ways: pitch as a rise over 12 (6/12), an angle in degrees (26.57), and a slope as a percentage (50%). This calculator converts between all three and then uses the pitch for the numbers a roofing or framing job needs.
Enter what you have. Type a pitch, an angle, or a rise and run measured on the roof or with a level and tape. The rise and run can be in any unit as long as both use the same one. The pitch is 12 times the rise divided by the run.
Rafter length. A common rafter is the sloped side of a right triangle: its length is the run times the square root of 1 plus (pitch / 12) squared. For a gable, the run is half the building's width. Add an overhang, measured horizontally, and it is lengthened by the same factor. The result is shown in feet and inches to the nearest 1/16 inch and in meters. It is the line length along the rafter, before the ridge, plumb and seat cuts.
Roof area and squares. The same factor, the pitch multiplier, turns the footprint of the roof (its plan area, overhangs included) into the sloped area. That holds for any roof whose planes share one pitch, hips and valleys included. Roofing is ordered in squares of 100 square feet; add a waste allowance for cutting, starter rows and ridge caps, commonly around 10 percent for a simple gable and more for a cut-up roof.
Bundles. Standard shingles often come 3 bundles to a square, while heavier architectural shingles may need 4 or more. Check the wrapper and set the number.
What this calculator does not do: it does not handle roofs with more than one pitch in a single calculation, hip and valley rafter lengths, or dormers, and it does not say which pitch a roofing material or local code allows. Check the shingle maker's instructions and your local building department.
A 6/12 roof rises 6 inches for every 12 inches of horizontal run. The angle is the arctangent of 6 divided by 12, which is 26.57 degrees, and the slope is 50 percent. A 4/12 roof is 18.43 degrees, an 8/12 roof is 33.69 degrees and a 12/12 roof is exactly 45 degrees.
Multiply the run by the square root of 1 plus the pitch over 12, squared. For a 12-foot run at 6/12, the factor is the square root of 1.25, or 1.118, so the rafter is 13.42 feet, about 13 feet 5 inches. Add any horizontal overhang to the run first.
Multiply the roof's footprint by the pitch multiplier to get the roof area, divide by 100 to get squares, and add waste. A 1,500 square foot footprint at 6/12 is 1,677 square feet, or 16.8 squares; with 10 percent waste that is 18.5 squares, or 56 bundles at 3 bundles a square.
A pitch multiplier is the ratio of the sloped roof area to its flat footprint, equal to the square root of 1 plus the pitch over 12, squared. It is 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12 and 1.414 at 12/12. Multiplying the footprint by it gives the roof area.
Hold a level horizontally against the roof or a rafter, mark 12 inches along the level, and measure straight up from that mark to the roof surface. That distance in inches is the pitch over 12. You can also measure any rise and run, enter both, and the calculator converts them.
The two words are often used interchangeably. Strictly, slope is the rise over the run, written as x/12 or as a percentage, while pitch has at times meant the rise over the full span. Most US roofers and codes now say pitch or slope for the same x/12 figure, which is what this calculator uses.
Formula only: no rates or limits are read from an official source.
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Also works as: Rafter Length Calculator.