Roof Pitch Calculator: Pitch, Angle, Slope % and Roof Area
Quick answer: a 6/12 roof rises 6 inches for every 12 inches across. That is an angle of 26.6° and a slope of 50%. Its pitch multiplier is 1.118, so a 1,500 sq ft footprint (including overhangs) has about 1,677 sq ft of roof, or 16.8 squares.
Roof pitch calculator
Roof pitch chart
How to measure roof pitch
- Put a level against the roof surface (or under a rafter in the attic) and hold it flat.
- Measure 12 inches along the level from the point where it touches the roof.
- Measure straight up (or down) from that 12" mark to the roof. That number is the pitch: 6 inches means 6/12.
Which pitch for which roofing?
| Pitch | What it means for roofing |
|---|---|
| Below 2/12 | Low-slope roofing only (membrane, built-up roof). Not for asphalt shingles. |
| 2/12 to under 4/12 | Asphalt shingles allowed with double underlayment under the IRC. |
| 4/12 and up | Standard shingle installation. |
| Above about 9/12 | Steep: roofers usually need roof jacks and harnesses, which can raise labor cost. |
Engineer's note: pitch also changes the loads. Steeper roofs shed snow better, but catch more wind. Rafter span tables in the IRC are set by the roof load and the rafter's horizontal span, not its sloped length, which is why this calculator gives both.
Common questions
What is the most common roof pitch?
Most US houses fall between 4/12 and 9/12. A 6/12 roof is a common middle ground.
How do I convert pitch to degrees?
Angle = arctan(rise ÷ 12). For example, 4/12 is arctan(0.333) = 18.4°.
What is a pitch multiplier?
The number you multiply flat (plan) area or horizontal run by to get the true sloped length or area: √(1 + (rise ÷ 12)²).
Checked by: Engr. Abdul Latif, civil and structural engineer. Geometry is exact; roofing slope limits follow IRC Section R905.2.2. Estimates for planning only.