Geometry / Construction / Measurement

Roof Pitch Calculator

Calculate roof pitch from rise and run. Convert the slope into pitch per 12, slope percentage, roof angle, rafter-length multiplier, and an estimated sloping rafter length.

Enter roof measurements

Enter positive values for the vertical rise and horizontal run.

Roof rise Vertical height difference.

Horizontal run Horizontal distance.

Rise and run units Rise and run must use the same unit.

Horizontal rafter run Horizontal distance used to estimate rafter length.

Rafter run unit

Decimal precision

Reset

Roof pitch results

Calculated values and right-triangle geometry.

                   /|
                  / |
      Rafter     /  | Rise
                /   |
               /    |
              / θ   |
             /______|
                Run

Submit the form to calculate the roof pitch and see the results here.

Example: rise 6 and run 12 gives a 6:12 pitch, 50% slope, an angle of about 26.565°, and a rafter multiplier of about 1.1180.

Roof pitch formulas

Roof pitch describes the vertical rise relative to the horizontal run. The calculator uses these standard right-triangle relationships.

Slope = Rise / Run Slope percentage = (Rise / Run) × 100 Pitch per 12 = (Rise / Run) × 12 Angle = arctan(Rise / Run) Multiplier = √(1 + Slope²) Rafter length = Horizontal run × Multiplier

Rise and run must use the same unit for the pitch calculation. The final rafter length uses the separate horizontal run and unit entered in the form.

Common roof pitch examples

Pitch	Slope	Angle
2:12	16.67%	9.46°
3:12	25.00%	14.04°
4:12	33.33%	18.43°
6:12	50.00%	26.57°
8:12	66.67%	33.69°
12:12	100.00%	45.00°

These examples express rise for every 12 units of horizontal run.

Frequently asked questions

Is a 6:12 pitch equal to a 50% slope?

Yes. Six divided by twelve is 0.5, which equals a 50% slope. The angle is approximately 26.565 degrees.

Does changing units change the roof pitch?

No. If rise and run are converted consistently, their ratio remains the same. The pitch, percentage, angle, and multiplier are unchanged.

Does this calculate the full roof area?

No. This tool calculates roof slope geometry and rafter length. Use a roof area calculator to estimate the sloping surface area.

Does the rafter length include an overhang?

Only if the horizontal run you enter already includes the overhang's horizontal projection. No construction allowance is added automatically.

Practical note

The result is a geometric estimate, not a structural engineering recommendation. Actual rafter dimensions may depend on span, loads, material, support conditions, connections, local regulations, and construction details.