Roof pitch describes how steep a roof is. In the U.S. it is written as rise over 12: a 6/12 roof rises 6 inches for every 12 inches it runs horizontally. This roof pitch calculator converts any rise and run into pitch, angle in degrees, slope percentage and the pitch multiplier, and — if you enter the building's footprint — the actual roof surface area and the number of roofing squares to order.
You can measure rise and run in any unit; only the ratio matters. A common method is to hold a level horizontally against a rafter or the roof surface, mark 12 inches along the level, and measure straight down (or up) to the roof. Planning other parts of the project? The concrete slab calculator and gravel calculator handle foundations and bases.
How to use the roof pitch calculator
- Measure the rise (vertical change) and run (horizontal distance) on the same slope. Using a 12 inch run gives the pitch directly.
- Enter both values; switch units if you measured in feet or centimetres.
- Read the pitch as x/12, the angle in degrees and the slope as a percent.
- For material estimates, enter the roof footprint — the plan area of the house including overhangs — to get the sloped surface area and squares (1 square = 100 ft²).
Formula
The multiplier is the length of the sloped rafter per unit of horizontal run (Pythagoras). Because every part of a uniformly pitched roof — gables and hips alike — rises at the same rate, multiplying the plan area by the multiplier gives the sloped surface area.
Worked example
You measure 6 inches of rise over a 12 inch run, and the house footprint with overhangs is 1,500 ft².
- Pitch: 6 ÷ 12 × 12 = 6/12.
- Angle: arctan(0.5) = 26.57°.
- Slope: 0.5 × 100 = 50%.
- Multiplier: √(1 + 0.25) = 1.1180.
- Roof area: 1,500 × 1.1180 = 1,677 ft² = 16.77 squares. Roofers then add waste for starter, ridge and cuts, often around 10–15%.
Roof pitch to angle chart
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.0035 |
| 2/12 | 9.46° | 16.7% | 1.0138 |
| 3/12 | 14.04° | 25.0% | 1.0308 |
| 4/12 | 18.43° | 33.3% | 1.0541 |
| 5/12 | 22.62° | 41.7% | 1.0833 |
| 6/12 | 26.57° | 50.0% | 1.1180 |
| 7/12 | 30.26° | 58.3% | 1.1577 |
| 8/12 | 33.69° | 66.7% | 1.2019 |
| 9/12 | 36.87° | 75.0% | 1.2500 |
| 10/12 | 39.81° | 83.3% | 1.3017 |
| 12/12 | 45.00° | 100.0% | 1.4142 |
Three ways to find your roof pitch
- From the attic. Hold a level horizontally against the underside of a rafter, mark 12 inches from where it touches, and measure vertically from that mark up to the rafter. That measurement is the rise in x/12.
- From the gable end. Measure the total rise from the top plate to the ridge and the horizontal run from the outside wall to the centre of the ridge. Enter both; the calculator scales them to x/12.
- With a phone or angle finder. Measure the angle of a rafter or the roof surface, then use the chart above to convert degrees back to pitch — for example, about 33.7° is an 8/12 roof.
Because pitch is a ratio, the run does not have to be 12 inches. A rise of 3 ft over a run of 9 ft gives 3 ÷ 9 × 12 = 4/12.
Caveats and assumptions
- Roofing products have minimum slopes. Many asphalt shingle manufacturers require at least 2/12 with special underlayment for 2/12–4/12; check the product instructions and your local code.
- Roofs with different pitches on different planes must be calculated plane by plane.
- The squares figure is surface area only. Add waste and accessories (starter, ridge cap, flashing) to your order.
- Never measure on a roof without proper fall protection; measure from the attic or a ladder at the eave where possible.
Frequently asked questions
What angle is a 6/12 roof pitch?
A 6/12 pitch is about 26.57 degrees, a 50% slope, with a pitch multiplier of 1.118.
How do I convert roof pitch to degrees?
Divide the rise by the run (e.g. 4 ÷ 12 = 0.333), take the arctangent, and convert to degrees: arctan(0.333) = 18.43°.
What is the most common roof pitch?
Pitches from about 4/12 to 9/12 are typical for homes in the U.S.; NRCA classes roofs above 3/12 as steep-slope.
How many squares is my roof?
Multiply the footprint area (including overhangs) by the pitch multiplier, then divide by 100. A 2,000 ft² footprint at 8/12 (multiplier 1.2019) is about 24 squares before waste.
What is the difference between pitch and slope?
They describe the same steepness. Pitch is usually written as rise per 12 inches of run (6/12); slope is often expressed as a percentage (50%) or an angle (26.57°).
Sources
- National Roofing Contractors Association (NRCA) — roof slope classifications and installation guidance
- NIST — Unit Conversion
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.