Enter the rise and the horizontal run of your roof to get the pitch as a ratio like 6:12, plus the slope percentage and the angle in degrees. Switch between inches and centimetres. The result is for planning, so work from drawings or measurements taken from the ground.
This calculator needs JavaScript. The formula and a worked example are below.
How to use the roof pitch calculator
Pitch compares how far a roof climbs (the rise) with how far it travels sideways (the run). Pick any pair of measurements that share the same unit. Rise 6 over run 12 gives a 6:12 roof.
You do not need a ladder. The easiest safe source is a drawing of the gable end. Or measure the roof angle from the ground in a photo taken straight on, then use the chart below to match it.
The formula
Slope = rise ÷ run. Slope percentage = slope × 100. Angle in degrees = arctan(slope) × 180 ÷ π. The pitch ratio is the slope multiplied by 12, written over 12.
Use the horizontal run, not the length of the rafter. Mixing those up is the most common reason a roof looks steeper in the numbers than it does on the house.
Worked example
A shed roof rises 6 inches for every 12 inches of run. The slope is 6 ÷ 12 = 0.5, so the pitch is 6:12 and the slope is 50%. The angle is arctan(0.5), which is 26.57 degrees. The surface multiplier is √(1 + 0.5²) = 1.118, so a flat 100 sq ft footprint becomes about 112 sq ft of roof.
Common roof pitches
| Pitch | Slope | Angle |
|---|---|---|
| 3:12 | 25% | 14.04° |
| 4:12 | 33.3% | 18.43° |
| 6:12 | 50% | 26.57° |
| 8:12 | 66.7% | 33.69° |
| 10:12 | 83.3% | 39.81° |
| 12:12 | 100% | 45° |
Pitch affects which materials are suitable, how the roof drains and how hard it is to work on. Always check the manufacturer’s minimum pitch for the roofing product you plan to use.
Frequently asked questions
What does 6:12 mean?
The roof rises 6 units for every 12 units of horizontal distance. The unit can be inches, centimetres or anything else, as long as both numbers use the same one.
How do I convert pitch to degrees?
Divide rise by run, then take the arctangent and convert to degrees. This calculator does it for you.
Is a higher pitch always better?
No. Steeper roofs shed water and snow faster but cost more to build and are harder to work on safely. The right pitch depends on climate, materials and the style of the house.
Can I measure pitch from the ground?
You can estimate it from a straight-on photo of the gable end or from building plans. Do not climb onto a roof just to measure it.
Related guides
See the different shapes in types of roof, or read the residential roofing guide before you hire anyone. Once you know the pitch, use the roof area calculator to estimate how much surface needs covering.