siteworkcalcMatch rise to run
Use the vertical change and horizontal distance between the same points. A 6 in rise over a 12 in run gives the same slope as 3 ft over 6 ft. Do not measure run along the roof surface.
BUILDING & ROOFING / TOOL 06
Roof Pitch Calculator.
One roof slope, every useful notation.
Convert rise and run to pitch, degrees and percent, with the geometry explained.
01 / YOUR MEASUREMENTS
Describe your roof slope
02 / YOUR SLOPE
Pitch, angle and geometry
Enter a measurement to see the same slope in different units.
Rise per 12 units of horizontal run
:12
Measure the horizontal and vertical distances
Convert the notation
Enter a measured rise/run, an X:12 pitch, an angle, or a percentage. The result reports all four forms. Switching measurement units preserves the physical dimensions.
Scale to your project
A short measurement segment tells you the slope, not the full rafter length. Add the actual horizontal project run to estimate its geometric rise and sloping length.
THE CALCULATION
The right triangle behind the pitch
Ratio = rise ÷ horizontal runPitch = (ratio × 12):12 · Slope % = ratio × 100Angle = arctan(ratio) × 180 ÷ πPitch factor = √(1 + ratio²)Geometric sloping length = horizontal project run × pitch factor. Rise = project run × ratio. Sloping area = horizontal projected area × pitch factor, for a plane of constant pitch. Units for rise and run must match.
6 inches up, 12 inches across
The ratio is 0.5, giving a 6:12 pitch, 26.5651°, 50% slope and a 1.118034 pitch factor.
For a separate 10 ft horizontal project run, the rise is 5 ft and geometric sloping length is 11.1803 ft. A 1,000 ft² horizontal roof projection at that pitch has 1,118.034 ft² of sloping area, before roofing waste.
Roof pitch conversion chart
Mathematical conversions, not recommended pitches or product approvals.
| Pitch | Angle | Slope | Factor |
|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.0035 |
| 2:12 | 9.46° | 16.67% | 1.0138 |
| 3:12 | 14.04° | 25.00% | 1.0308 |
| 4:12 | 18.43° | 33.33% | 1.0541 |
| 5:12 | 22.62° | 41.67% | 1.0833 |
| 6:12 | 26.57° | 50.00% | 1.1180 |
| 8:12 | 33.69° | 66.67% | 1.2019 |
| 10:12 | 39.81° | 83.33% | 1.3017 |
| 12:12 | 45.00° | 100.00% | 1.4142 |
Use the result in the right context
Run is not span
For a symmetrical gable, the horizontal run from eave to ridge is half the full eave-to-eave span. For a single-slope shed roof, use the horizontal distance between its high and low endpoints. Never halve a measurement that already represents run.
Line length is not cut length
The sloping length is the hypotenuse between your chosen points. Overhangs, ridge thickness, birdsmouth details and joints affect the stock and cuts you need. After those dimensions are established, use the Board Foot Calculator to tally lumber volume and cost.
Area is a separate estimate
Multiply horizontal roof projection area by the pitch factor for one plane, or planes of equal pitch. Measure different pitches separately. The result excludes material overlap, cutting waste and packaging; it is not a shingle order.
FIELD NOTES
Common questions
What is a 6/12 roof pitch in degrees?
A 6:12 pitch has a rise/run ratio of 0.5. Its angle is arctan(0.5) = 26.5651°, and its slope is 50%. It is not a 6° angle or a 6% slope.
Are roof pitch and slope the same?
This calculator uses the common X:12 rise-over-run convention. In some traditional terminology, “pitch” instead means rise divided by the full roof span. Confirm the notation used on your plans before entering a value.
Can this choose a minimum roof pitch?
No. Geometry alone cannot establish suitability for a roofing product, structural loads or drainage. Check the applicable product specifications and project design. A zero result means a geometrically level plane, not an approved roof design.
Can I measure roof pitch with my phone?
You can enter an angle measured by an appropriate instrument, but this tool does not access a phone’s sensors or calibrate them. Use plans or safely obtained measurements; do not climb onto a roof to use the calculator.
METHOD & REFERENCES
Sources and assumptions
Reviewed October 21, 2026. Right-triangle geometry, arctangent and unit conversions. No structural design, material suitability or minimum-pitch recommendation is inferred.