Roof pitch is the relationship between vertical rise and horizontal run. Measure one roof section at a time, and record whether the measurement came from the roof, attic, drawing, or another source.
What to measure
Measure one roof section at a time. Rise is the vertical change; run is the horizontal distance over the same section. A cross-gable, hip, gambrel, or other complex roof can contain different pitches, so record each section before adding areas or material quantities.
The formula
slope = rise ÷ run; pitch = 12 × slope; angle = atan(slope) × 180 ÷ π
- Rise
- Vertical measurement in the selected unit.
- Run
- Horizontal measurement in the selected unit.
- Pitch
- Rise normalized to 12 inches of run.
Rise and run can use different units because the calculator converts each value before comparing the ratio.
The same slope can be described as a ratio, a percentage, or an angle. Those are different descriptions of one measured right triangle; they do not identify the pitch of every roof section automatically.
How to measure a roof section
- Choose one roof section and identify a horizontal run and vertical rise that belong to it.
- Measure rise and run with a level, tape, framing reference, attic measurement, or a reliable drawing.
- Record the unit beside each measurement. Do not combine a rise from one section with a run from another.
- Enter rise and run in the Roof Pitch Calculator, or clear both fields before using the angle alternative.
- Split the roof into separate sections when the slopes, geometry, or measurement sources differ.
| Description | What it means |
|---|---|
| 6:12 pitch | 6 inches of rise for every 12 inches of horizontal run |
| 0.50 decimal slope | Rise divided by run |
| 50% slope | Decimal slope multiplied by 100 |
| 26.57° angle | The angle of the measured right triangle |
Worked example
Inputs: Rise = 6 in; run = 12 in.
Calculation: 6 ÷ 12 = 0.5 slope. 0.5 × 12 = 6, so the pitch is 6:12. atan(0.5) × 180 ÷ π = 26.565051°.
Result: The calculator displays 6.00:12, 0.5000, 50.00%, and 26.57°.
Rounding: The ratio is kept at full precision during the calculation. The angle is displayed to two decimal places and the decimal slope to four.
Use the result to compare measurements and choose the next planning tool. It does not approve a roofing product, prove code compliance, or replace a site assessment.
When to split sections
Use separate measurements for roof planes with different pitches, dormers, valleys, hips, or changes in run. Calculate the area of each applicable plane separately before combining quantities. The roof-area calculator is intended for a simple rectangular section with one consistent pitch.
The pitch result is a measurement aid. Product instructions, local requirements, structural decisions, and the condition of the roof remain outside this arithmetic.