Roof Pitch Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
A roof's pitch is calculated with (rise ÷ run) × 100 for a percentage, or the arctangent of that same ratio for an angle in degrees. For a rise of 2 m and a run of 4 m, the pitch is 50%, or about 26.6°.
Explanation
A roof's pitch expresses its slope, in two forms commonly used in construction: as a percentage (the ratio of vertical rise to horizontal run covered, multiplied by 100) or in degrees (the actual angle from horizontal). The two aren't proportional: a 100% pitch doesn't correspond to a 100° angle, but to exactly 45°, the point where rise and run are equal. In practice, percentage remains the most widely used unit on plans and quotes, while degrees are more intuitive for visualizing the actual slope. The choice of roof pitch depends heavily on the type of roofing (tiles, slate, green roof, metal sheeting...) and local building codes, since each material has a minimum pitch to ensure watertightness — a technical detail specific to each material, not covered by this calculator. For the area of a room or a wall, see our area calculator.
Example: a rise of 2 m, a run of 4 m
Inputs
Rise: 2 m. Run: 4 m.
Calculation
Pitch in % = (2 ÷ 4) × 100 = 50%. Pitch in degrees = arctan(2 ÷ 4) = arctan(0.5) ≈ 26.57°.
Result
The pitch of this roof slope is 50%, or about 26.6°.
Frequently asked questions
Why doesn't a 100% pitch correspond to 90°?
Because percentage and degrees measure pitch differently: 100% means the rise equals the run (a ratio of 1), which corresponds to a 45° angle, not 90°. A 90° angle (a vertical slope) would correspond to an infinite pitch in percentage, since the horizontal run would approach zero.
What minimum pitch is needed for tiles or slate?
That depends heavily on the type of tile or slate and the region (exposure to wind and rain): manufacturers specify a minimum pitch to guarantee their product's watertightness, generally between 30% and 45% for common tiles in a temperate climate, but this varies significantly from one product to another. Always check the spec sheet for the chosen material rather than relying on a general rule.
How do I measure the rise and run on an existing roof?
The rise is the difference in level between the low point (eave) and the high point (ridge) of the same roof slope, and the run is the horizontal distance between those same two points, measured on the ground or from a plan. On a framing plan, these two values are generally already given; on an existing roof, they're measured or derived from the building's plans.