Roof Pitch Calculator
Work out roof pitch as x in 12, degrees and percentage, plus rafter length with overhang, roof area in m² and ft², and roofing squares.
Reviewed by Dany, RightSums team · Updated
Runs in your browser. Free, no sign-up.
home-energy · Daily life · UK & US
Enter the pitch in whichever form you have it: x in 12, an angle in degrees, or a rise and run you have measured. The calculator converts it to all three, along with the pitch multiplier, the number that turns level run into sloping length. Add the building width, length and overhangs to get the common rafter length with and without the eaves, the ridge height and the roof area in square metres, square feet and 100 ft² roofing squares. For a hip roof it also gives the hip rafter length and the shorter ridge. A 6/12 roof is 26.57° with a multiplier of 1.118. Sizes work in metres and millimetres or feet and inches, and every length is shown in both.
Accepted inputs
- Roof type (gable or hip)
- Pitch as x in 12
- Pitch as an angle in degrees
- Rise and run
- Building width and length
- Eaves and gable end overhangs
- Metric or imperial units
Outputs
- Pitch as x:12 and x in 12
- Angle in degrees
- Percentage slope
- Pitch multiplier
- Common rafter length with overhang
- Hip rafter length
- Ridge height and ridge length
- Roof area in m² and ft²
- Roofing squares
How to use the Roof Pitch Calculator
- Choose a gable or hip roof and pick metric or imperial units.
- Enter the pitch as x in 12, as an angle in degrees, or as any rise and run you have measured.
- Add the building width, length and overhangs, and the calculator halves the width to find the rafter run and multiplies it by the pitch multiplier.
- It then multiplies the footprint, overhangs included, by the same multiplier to give the roof area in square metres, square feet and roofing squares.
Frequently asked questions
What angle is a 6/12 roof pitch?
A 6/12 roof is 26.57 degrees, a 50% slope. It rises 6 inches for every 12 inches of level run, and its pitch multiplier is 1.118, so each metre or foot of run becomes 1.118 along the rafter. For comparison, 4/12 is 18.43 degrees and 12/12 is 45 degrees.
How do I calculate rafter length?
Halve the building width to get the run, add the eaves overhang, then multiply by the pitch multiplier. A 24 ft wide house at 6/12 with 12 in eaves needs 13 ft x 1.118 = 14 ft 6 3/8 in. An 8 m wide house at 35 degrees with 300 mm eaves needs 4.3 m x 1.221 = 5.25 m.
How do I work out the area of a roof?
Multiply the footprint, overhangs included, by the pitch multiplier. An 8 m by 10 m house with a 35 degree gable roof and 300 mm eaves has 8.6 x 10 x 1.221 = 105.0 m² of roof, or 1,130 ft². With a hip roof and a 300 mm overhang on all four sides it is 111.3 m².
How many roofing squares do I need?
A roofing square is 100 ft² of roof surface. A 24 by 40 ft house with a 6/12 gable roof and 12 in eaves has 1,163 ft² of roof (108.0 m²), which is 11.63 squares. That figure has no allowance for waste, ridge caps or starter courses, so ask your supplier how much extra to order.
What is the minimum pitch for a roof?
It depends on the covering, and the maker's installation instructions set the lowest pitch for each product. In the US, the International Residential Code (R905.2.2) only allows asphalt shingles from 2 in 12, about 9.5 degrees, and needs double underlayment up to 4 in 12. The calculator flags those US limits but checks no other covering.
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