Roof Pitch Calculator
This roof pitch calculator converts pitch to angle and percent slope, then uses the slope multiplier to turn your footprint into real roof area.
A 6:12 roof rises 6 inches for every 12 inches of run: a 26.57° angle, a 50% slope and a 1.118 area multiplier. A 1,500 sq ft footprint therefore has about 1,677 sq ft of roof, or 16.8 squares of shingles, before waste.
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How to calculate roof pitch
Roof pitch is how steep a roof is, written as rise over run, almost always over a 12 inch run in the U.S. A 6:12 roof rises 6 inches for every 12 inches of horizontal distance. The same slope can be an angle in degrees or a percent grade.
percent slope = rise ÷ 12 × 100
slope multiplier = √(rise² + 144) ÷ 12
roof area = footprint × multiplier
Example: 6:12 gives arctan(0.5) = 26.57°, a 50% slope and a multiplier of √(36 + 144) ÷ 12 = 1.118. A 1,500 sq ft footprint is 1,677 sq ft of roof, which is 16.8 squares.
Pitch chart
| Pitch | Angle | Slope | Area multiplier |
|---|---|---|---|
| 2:12 | 9.5° | 16.7% | 1.0138 |
| 3:12 | 14.0° | 25.0% | 1.0308 |
| 4:12 | 18.4° | 33.3% | 1.0541 |
| 5:12 | 22.6° | 41.7% | 1.0833 |
| 6:12 | 26.6° | 50.0% | 1.1180 |
| 7:12 | 30.3° | 58.3% | 1.1577 |
| 8:12 | 33.7° | 66.7% | 1.2019 |
| 9:12 | 36.9° | 75.0% | 1.2500 |
| 10:12 | 39.8° | 83.3% | 1.3017 |
| 12:12 | 45.0° | 100.0% | 1.4142 |
Why it matters
- Steeper roofs have more surface area for the same footprint, so they cost more to cover.
- Low-slope roofs below about 2:12 or 4:12 may need special membranes; shingle makers state a minimum pitch, so check the product.
- Steep roofs are harder and more dangerous to work on.
With the true area in hand, use the roofing calculator for bundles of shingles, and the square footage calculator to measure the footprint.
Frequently asked questions
How do you calculate roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run. If it rises 6 inches, the pitch is 6:12.
What is a 6/12 roof pitch in degrees?
About 26.57 degrees, a 50% slope.
What is the roof pitch multiplier?
The factor that converts footprint to roof area: √(rise² + 144) ÷ 12. For 6:12 it is 1.118.
What is a normal roof pitch?
Residential roofs commonly fall between about 4:12 and 9:12.
How many squares is my roof?
Divide the true roof area by 100 square feet. A 1,677 sq ft roof is 16.8 squares.
Sources and further reading
- Roof slope multiplier — InterNACHI
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
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. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.