Roof pitch calculator
From rise and run to the right roof angle.
Pitch preview
Section AHave rise and run?
Use the same unit for both measurements.
The math behind the angle
Angle = arctan(pitch ÷ 12)
Area factor = √(1 + (pitch ÷ 12)²)
Use horizontal run, not the sloped rafter length. A 6:12 pitch is a 50% slope and a 26.6° angle.
Use this pitch in your roof planRoof measurements
Section A: gable, 40.00 × 30.00 ft; overhang 12.0 in; pitch 6.00:12.
Waste: 10%. Planning quantities only; verify before ordering.
Understanding roof pitch, angle and slope
Roof pitch is expressed here as rise for every 12 units of horizontal run. It is a ratio, so 6 inches over 12 inches and 50 centimeters over 100 centimeters describe the same slope.
Is 6:12 the same as 6 degrees?
No. A 6:12 pitch means a rise equal to half the horizontal run. Its angle is about 26.6 degrees.
How do I convert degrees to pitch?
Multiply the tangent of the angle by 12. For example, tan(45°) × 12 = 12, so a 45-degree roof has a 12:12 pitch.
Can this calculate structural rafter lengths?
This calculator estimates slope and surface area only. Structural rafter sizing, load capacity, ridge details and cutting allowances require a separate design.
How should I measure the roof?
Use existing plans or measurements taken from a safe, accessible position. You do not need to climb onto a roof to use this calculator.