JB PARCELRoof Pitch Calculator
Enter the rise per foot and the roof outline seen from above. Get the angle, the real surface area of the slopes, and the squares and shingle bundles to order, so you can check a roofing bid before you sign it.
How this calculator works
Pitch is rise over run, always stated per 12 inches of horizontal run. A 6/12 roof climbs 6 inches for every foot it runs, which is an angle of about 26.6 degrees. The angle is the arctangent of rise divided by 12.
A sloped roof has more surface than the footprint it covers. The pitch multiplier converts one to the other: it is the square root of one plus the rise over run squared. For a 6/12 roof that is about 1.118, so a 2,000 square foot footprint carries roughly 2,236 square feet of roof.
Divide the surface area by 100 to get squares, the unit roofers bid and shingles are sold in, then add waste for cutting. Around 10 percent covers a simple gable. Hip roofs, valleys, and dormers cut more shingles and need more. Most shingles come three bundles to a square.
Use the footprint of the roof, not the house. Overhangs at the eaves and rakes add real area, and a porch or garage under the same roof counts too. Measuring the roof outline from above, or from an aerial image, is how estimators get it.
Worked example: checking a reroof bid on a ranch house
A 5/12 hip roof with a 2,150 sf footprint including overhangs, and a 12 percent waste allowance for the hips.
| Roof angle | 22.6 degrees |
|---|---|
| Pitch multiplier | 1.083 |
| Roof surface area | 2,329 sf |
| Squares, waste included | 26.1 |
| Shingle bundles | 79 |
If the bid prices 32 squares, ask where the extra six came from. It may be a second layer to tear off or a detached garage, which are real. It may also be padding. Either way you now know which question to ask.
Where the numbers come from
Pitch, angle, and area are geometry. The asphalt shingle slope limits are from the International Residential Code, section R905.2.2. Manufacturer installation instructions can be stricter and control the warranty.
Questions investors ask
How do I measure roof pitch?
Hold a level horizontally against the roof surface, mark 12 inches along it, and measure straight up from that mark to the roof. That measurement in inches is the rise. A 4 inch reading means a 4/12 pitch. You can also measure the same way on a rafter in the attic.
What is a 6/12 roof pitch in degrees?
About 26.6 degrees. A 4/12 is about 18.4 degrees, 8/12 is about 33.7, and 12/12 is exactly 45.
What is a roofing square?
100 square feet of roof surface. A roof with 2,236 square feet of surface is about 22.4 squares before waste. Roofers bid and suppliers sell by the square.
How many bundles of shingles are in a square?
Usually three. Some heavier designer shingles take four or more. The wrapper states coverage per bundle, so divide 100 by that figure if you are unsure.
What is the lowest pitch you can put shingles on?
The International Residential Code allows asphalt shingles down to 2/12, and requires a double layer of underlayment between 2/12 and 4/12. Below 2/12 you need a low-slope system such as a membrane. The shingle manufacturer's instructions can be stricter and govern the warranty.
Related calculators
Screening a real property? Pull its appraised value, assessed value, acreage, land use, and last recorded sale off the JB PARCEL parcel map and drop the real numbers into this calculator instead of guessing. Coverage runs across every county we carry.