Enter rise and run in the same unit. The calculator derives the angle using trigonometry, reports percent slope and shows the slope-length multiplier that converts horizontal run to sloped length. A 12-unit run is common for describing roof pitch, but the math works for any consistent rise and run.
Calculate
- Angle = arctangent(rise ÷ run).
- Percent slope = rise ÷ run × 100.
- Area multiplier = square root(rise² + run²) ÷ run.
- This is a geometry tool; material minimum slopes and local roofing requirements must be checked separately.
Roof pitch geometry
Rise, run, angle and slope factor are linked by one right triangle.
Roof pitch conversions you can verify at a glance
Rise/run, angle and slope factor are different representations of the same roof-plane geometry. The interactive calculator is the working tool; this table is the audit check.
| Pitch | Approx. angle | Slope factor |
|---|---|---|
| 2:12 | 9.5° | 1.014× |
| 4:12 | 18.4° | 1.054× |
| 6:12 | 26.6° | 1.118× |
| 8:12 | 33.7° | 1.202× |
| 10:12 | 39.8° | 1.302× |
| 12:12 | 45.0° | 1.414× |
How to use this page
Measure the project before entering values, keep units consistent, and review the assumptions shown with the result. The calculator is designed to expose the math it can perform and to stop before making a local-code, product-selection or professional-design decision it cannot support.
For irregular geometry, divide the project into simple sections, calculate each section separately and add the results. When a supplier, product label, plan set or project specification provides a value that differs from an example, use the project-specific value.
Public corpus v1 · Method and scope reviewed for launch on 2026-08-13.
Convert rise and run into roof pitch, angle and slope factor
Roof pitch describes the relationship between vertical rise and horizontal run. This calculator turns that geometry into equivalent forms so the same measurement can be used for roof-area, sheathing and roofing-material calculations.
Rise, run and angle describe the same slope in different ways
A pitch such as 6:12 means the roof rises 6 units for every 12 units of horizontal run. The slope ratio can be converted to an angle with trigonometry, and a slope factor converts horizontal plan length or area to sloped length or area.
Keeping these forms together prevents a common mistake: treating horizontal footprint dimensions as though they were already measured along the roof surface.
angle = arctan(rise ÷ run); slope factor = √(rise² + run²) ÷ runMeasure the geometry you actually have
Pitch can be measured from framing, plans or a suitable level-and-rise method. The calculator converts the measurement; it does not verify that the measurement was taken from a straight, representative roof plane.
For roofs with multiple pitches, calculate each pitch separately. A single average pitch can hide meaningful differences in surface area and material quantities.
Pitch is geometry, not approval
A numerical pitch does not by itself determine whether a roof system is permitted or appropriate. Minimum slopes, underlayment, drainage, snow considerations and product limitations depend on the assembly, manufacturer instructions and applicable requirements.
Use the result to support geometry and quantity calculations, then check the project-specific rules separately.
Verify before you use the result
- Measure rise and run on the same scale.
- Split roofs with different pitches into separate planes.
- Check manufacturer and project requirements before using any roof covering at a given slope.
Questions that come up before the next step
What does a 6:12 roof pitch mean?
It means the roof rises 6 units vertically for every 12 units of horizontal run. The units can be inches, centimeters or another consistent unit because the pitch is a ratio.
Is roof pitch the same as roof angle?
They describe the same slope but use different notation. Pitch is usually rise over run; angle is measured in degrees.
Why do I need a roof pitch multiplier?
The multiplier converts horizontal dimensions to sloped dimensions. It is useful when estimating surface area for sheathing and roof-covering materials.
Primary and official references
Sources support the method and scope boundaries; project-specific requirements still need applicable product, supplier or local documentation.
Roof-system slope limits vary by system and project; slope is a design and drainage consideration.