Free tool · for homeowners, roofers and framers
Roof Pitch Calculator: Pitch, Angle, Slope, Rafter Length and Roof Squares
Know the rise and run, the angle, or the rise and building width? Get the pitch, angle and slope with a live drawing, plus rafter length, roof area, squares and shingle bundles for your whole roof.
Roof Pitch Calculator
Roof area uses the footprint with overhangs times the slope factor, which works for gable and hip roofs of one pitch. Rafter length is measured along the top edge before the ridge board deduction and plumb cuts. Most asphalt shingles come 3 bundles to a square (100 sq ft); check the wrapper.
How Do You Find the Pitch of a Roof?
Measure how many inches the roof rises over 12 inches of level run. A 6-inch rise per 12 inches is a 6/12 pitch, which is 26.6 degrees or a 50% slope. To get the roof area, multiply the building footprint with overhangs by the slope factor, 1.118 for a 6/12 roof.
Checked against the sources below · How we build and test our calculators
Roof Pitch Chart: Angle, Slope and Factor
Multiply the flat footprint by the slope factor to get the real roof surface.
| Pitch | Angle | Slope | Slope factor | Rafter per 10 ft of run |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 | 10.03 ft |
| 2/12 | 9.5° | 16.7% | 1.014 | 10.14 ft |
| 3/12 | 14° | 25% | 1.031 | 10.31 ft |
| 4/12 | 18.4° | 33.3% | 1.054 | 10.54 ft |
| 5/12 | 22.6° | 41.7% | 1.083 | 10.83 ft |
| 6/12 | 26.6° | 50% | 1.118 | 11.18 ft |
| 7/12 | 30.3° | 58.3% | 1.158 | 11.58 ft |
| 8/12 | 33.7° | 66.7% | 1.202 | 12.02 ft |
| 9/12 | 36.9° | 75% | 1.250 | 12.50 ft |
| 10/12 | 39.8° | 83.3% | 1.302 | 13.02 ft |
| 12/12 | 45° | 100% | 1.414 | 14.14 ft |
| 14/12 | 49.4° | 116.7% | 1.537 | 15.37 ft |
| 16/12 | 53.1° | 133.3% | 1.667 | 16.67 ft |
| 18/12 | 56.3° | 150% | 1.803 | 18.03 ft |
How to Measure Roof Pitch
- Use a 12-inch level (or mark 12 in on a longer one).
- Hold it level with one end touching the roof or the underside of a rafter.
- Measure straight up from the 12-inch mark to the roof. That number is the rise.
- Write it as rise/12. 5 inches = a 5/12 pitch.
Common Roof Pitches
- Under 2/12: flat or low slope, needs a membrane roof.
- 2/12 to 4/12: low slope; shingles need extra underlayment.
- 4/12 to 9/12: most US homes; easy to walk up to about 6/12.
- Over 9/12: steep; roofers need roof jacks and harnesses, which raises labor cost.
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Questions
How do I calculate roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run. Hold a level 12 inches long against the rafter or roof, and measure straight up from the end of the level to the roof. A 6-inch rise over 12 inches is a 6/12 pitch.
What is a 4/12 roof pitch in degrees?
About 18.4°. A 6/12 pitch is about 26.6°, 8/12 about 33.7°, and 12/12 is exactly 45°.
What is the difference between pitch and slope?
Pitch is usually written as rise over a 12-inch run, such as 6/12. Slope can mean the same ratio or the percentage grade: a 6/12 pitch is a 50% slope. The angle in degrees is a third way to describe it.
How do I find roof pitch from the ground or inside?
In the attic, measure the rafter’s rise over a 12-inch level. From the gable end outside, measure the total rise from the top of the wall to the ridge and the building width; enter both in “Rise and building width” mode.
What is the minimum pitch for asphalt shingles?
Most manufacturers and the International Residential Code allow asphalt shingles down to a 2/12 pitch, with double underlayment required between 2/12 and 4/12. Below 2/12, use a low-slope membrane roof.
What is a roofing square?
A square is 100 square feet of roof surface. Most asphalt shingles come 3 bundles to a square; check the wrapper for your product.
How do I calculate roof area from the footprint?
Multiply the footprint (including overhangs) by the slope factor for the pitch. For a 6/12 pitch the factor is 1.118, so a 26 × 42 ft footprint is about 1,221 sq ft of roof.