Roof Pitch Calculator and Chart

Rise vs. Run

Rise is the vertical change between two points on a roof slope. Run is the horizontal distance between those same points—not the distance along the sloping surface.

For a symmetrical gable measured from eave level to ridge, run is half the corresponding full span. Do not halve a measurement that is already the run.

Use corresponding measurements from plans or a qualified professional. Do not climb onto a roof to take measurements.

Reading a Pitch Ratio

A 4:12 pitch rises 4 inches for every 12 inches of horizontal run. The same proportion applies at any scale.

• 3:12: 3 inches of rise per 12 inches of run; approximately 14.04°.
• 6:12: 6 inches of rise per 12 inches of run; approximately 26.57°.
• 12:12: equal rise and run; 45°.

These are examples, not recommendations for a particular roof or roofing material.

How the Calculation Works

Pitch per 12 = rise ÷ run × 12.
Slope percentage = rise ÷ run × 100.
Angle = arctangent of rise ÷ run, expressed in degrees.

For example, 4 feet of rise over 8 feet of horizontal run gives a 6:12 pitch, 50% slope, and an angle of about 26.57°.

Both distances must use the same units. The calculator converts your feet-and-inches entries to inches before calculating.

Using Your Result

Use the calculated pitch to communicate roof geometry and compare it with product specifications. A non-whole-number pitch should not automatically be rounded up to select a bracket.

Confirm the actual pitch and fitting requirements before ordering. The result does not establish structural safety, roofing suitability, drainage performance, or snow-load capacity.

Sloping length is the straight-line distance between the measured points, not a finished rafter cut length.