Roof pitch is the ratio of the vertical rise to the horizontal run, always expressed per 12 inches of run in the US. The three values this calculator produces from a single rise/run input are:
Step-by-step measurement from the ground:
Once you know the actual roof surface area, the Asphalt Calculator shows how the same area-times-multiplier approach applies to tonnage estimates for asphalt shingle or metal panel projects.
Degrees are used in architectural drawings and structural specifications, while Rise/12 notation is used in the roofing trade. The formula is: Angle = arctan(Rise / Run) x (180 / pi). Every common Rise/12 pitch has an exact degree equivalent:
| Pitch (Rise/12) | Angle (degrees) | Multiplier | Category | Material |
|---|---|---|---|---|
| 1/12 | 4.8° | 1.003 | Nearly flat | Membrane only |
| 2/12 | 9.5° | 1.014 | Low slope: requires special materials | Membrane only |
| 3/12 | 14.0° | 1.031 | Low slope | Special shingles |
| 4/12 | 18.4° | 1.054 | Standard residential | Standard shingles |
| 5/12 | 22.6° | 1.083 | Standard residential | Standard shingles |
| 6/12 | 26.6° | 1.118 | Moderate | Standard shingles |
| 8/12 | 33.7° | 1.202 | Steep | Standard shingles |
| 12/12 | 45.0° | 1.414 | Very steep | Standard shingles |
To convert degrees back to Rise/12: Rise = tan(degrees) x 12. For a 26.6 degree roof: tan(26.6) x 12 = 0.5 x 12 = 6, which is a 6/12 pitch. This calculator shows both values automatically from a single rise/run entry.
The actual roof surface area is always larger than the floor footprint because the slope adds length. The pitch multiplier converts footprint to actual area. Ordering roofing materials without applying the multiplier will result in a shortage:
| Footprint | Pitch | Multiplier | Actual Area | Squares (+10% waste) |
|---|---|---|---|---|
| 1,000 sq ft | 4/12 | 1.054 | 1,054 sq ft | 12 squares |
| 1,000 sq ft | 6/12 | 1.118 | 1,118 sq ft | 13 squares |
| 1,000 sq ft | 8/12 | 1.202 | 1,202 sq ft | 14 squares |
| 1,500 sq ft | 5/12 | 1.083 | 1,624 sq ft | 18 squares |
| 2,000 sq ft | 6/12 | 1.118 | 2,236 sq ft | 25 squares |
| 2,000 sq ft | 8/12 | 1.202 | 2,404 sq ft | 27 squares |
For calculating the floor footprint of your home before applying the multiplier, the Square Footage Calculator handles rectangles, L-shapes, and irregular layouts with unit conversion built in.
Sheds, lean-tos, and single-slope (mono-pitch) roofs use the same formula as standard roofs. The key difference is that a lean-to has only one slope rather than two mirrored slopes. Use the full width of the lean-to as the run when calculating:
| Structure | Recommended Pitch | Notes |
|---|---|---|
| Small storage shed | 3/12 to 4/12 | Minimum for adequate drainage with metal or shingles |
| Large shed or barn | 4/12 to 6/12 | Allows loft space, good for snow load shedding |
| Lean-to / porch cover | 2/12 to 4/12 | Lower pitch keeps the structure low at the back wall |
| Bike or equipment cover | 2/12 to 3/12 | Minimal height, use metal or polycarbonate panels |
| Greenhouse lean-to | 3/12 to 5/12 | Enough slope to run rainwater off polycarbonate |
| Carport / car shelter | 3/12 to 4/12 | Clear span with adequate drainage |
For calculating materials for the interior of a shed (insulation, drywall panels, or wall sheeting), the Drywall Calculator accounts for wall area, doors, windows, and waste factor.
A 1,500 sq ft ranch home has a 5/12 roof pitch. How many roofing squares should be ordered?