Roof Pitch Calculator: Angle, Slope & Pitch Factor
Convert rise and run, X:12 pitch, roof angle, or percent slope. Get the matching pitch, degrees, slope percentage, and surface-area factor in one calculation.
Start with the roof measurement you already know.
Use rise and run, enter an X:12 pitch, enter an angle in degrees, or enter percent slope. The calculator converts the value into the other common roof-slope measurements.
Rise is vertical. Run is horizontal. The diagonal roof surface is not the run.
Check plans or accessible framing first. You often do not need to walk on the roof.
See safer measurement options ↓What does roof pitch mean?
Roof pitch describes how steep a roof is. In U.S. residential construction it is commonly written as vertical rise for every 12 units of horizontal run.
The roof rises 6 inches vertically for every 12 inches horizontally.
Start with options that do not require walking on the roof.
Roof access involves fall risk. Existing plans, accessible framing, a clear gable view, or professional measurement may provide the information you need.
Building or roof plans may already identify the slope as 4:12, 6:12, 8:12, or another pitch.
Where framing is safely accessible, a horizontal run and vertical rise can be measured from a rafter.
A clear side view may help establish roof geometry without treating the exterior roof as a measurement platform.
Complex, tall, or inaccessible roofs may be better measured by a qualified professional or measurement service.
Run is horizontal — not the diagonal roof length.
The run is measured horizontally. The sloped roof surface or rafter is the hypotenuse of the triangle and is longer than the run.
For a simple symmetrical gable roof, the horizontal run from the exterior wall to a point directly below the ridge is commonly half the building span.
The conversions come from one rise-to-run ratio.
The calculator uses standard right-triangle geometry. You can independently verify each result with these formulas.
(rise ÷ run) × 12
Converts any measured rise and run to standard rise-per-12 notation.
arctan(rise ÷ run)
Converts the rise/run ratio into an angle measured from horizontal.
(rise ÷ run) × 100
Expresses the same slope as a percentage.
√(1 + (rise ÷ run)²)
Converts horizontal plan area into approximate sloped surface area for a uniform roof plane.
Converting a 6:12 pitch
Pitch to degrees, percent slope and factor.
Use this table for fast reference or use the calculator for custom slopes that fall between these common values.
| Pitch | Angle | Percent slope | Pitch factor |
|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.003 |
| 2:12 | 9.46° | 16.7% | 1.014 |
| 3:12 | 14.04° | 25.0% | 1.031 |
| 4:12 | 18.43° | 33.3% | 1.054 |
| 5:12 | 22.62° | 41.7% | 1.083 |
| 6:12 | 26.57° | 50.0% | 1.118 |
| 7:12 | 30.26° | 58.3% | 1.158 |
| 8:12 | 33.69° | 66.7% | 1.202 |
| 9:12 | 36.87° | 75.0% | 1.250 |
| 10:12 | 39.81° | 83.3% | 1.302 |
| 11:12 | 42.51° | 91.7% | 1.357 |
| 12:12 | 45.00° | 100% | 1.414 |
| 14:12 | 49.40° | 116.7% | 1.537 |
| 16:12 | 53.13° | 133.3% | 1.667 |
Geometry, safety terminology and roofing requirements are not the same thing.
A calculator can identify the slope, but material installation requirements and jobsite safety rules depend on additional factors.
OSHA defines a low-slope roof as a roof with a slope less than or equal to 4:12. OSHA defines a steep roof as greater than 4:12.
Those definitions are used in workplace safety regulations; they are not a statement that a particular roofing material is suitable for every roof at that slope.
Some asphalt-shingle applications distinguish between lower-slope installations and standard-slope installations, including different underlayment requirements.
Always verify the current installation instructions for the exact roofing product and applicable local requirements.
Pitch converts horizontal footprint into sloped surface area.
A pitched roof covers more surface than the horizontal footprint beneath it.
For a simple roof plane represented by one consistent pitch:
Multiple roof pitches, dormers, hips, valleys, porches, additions, and other geometry can require separate measurements for each roof plane.
One pitch value may not describe the entire roof.
Homes can combine main roofs, porches, garages, dormers, additions, and other sections with different slopes.
Use the calculator for planning and comparison. Final material quantities, project scope, and pricing should be based on verified measurements and actual site conditions.
Common Questions About Roof Pitch
Quick answers to common pitch, angle, slope, measurement, and roof-area questions.
What is roof pitch?
Roof pitch describes the steepness of a roof. In U.S. residential construction it is commonly expressed as vertical rise for every 12 units of horizontal run. A 6:12 roof rises 6 inches for every 12 horizontal inches.
What does a 6:12 roof pitch mean?
A 6:12 roof pitch rises 6 inches vertically for every 12 inches of horizontal run. It equals approximately 26.57 degrees, a 50% slope, and a pitch factor of about 1.118.
What angle is a 4:12 roof pitch?
A 4:12 roof pitch is approximately 18.43 degrees. It equals a 33.3% slope and has a pitch factor of approximately 1.054.
How do I convert roof angle to pitch?
Take the tangent of the roof angle and multiply the result by 12. For example, tan(26.57 degrees) is approximately 0.5; multiplied by 12, that produces a 6:12 pitch.
How do I convert percent slope to roof pitch?
Divide the percent slope by 100 to get the decimal slope, then multiply by 12. A 50% slope equals 0.5; 0.5 multiplied by 12 equals a 6:12 pitch.
What is a roof pitch factor?
A pitch factor is the multiplier between horizontal run and the corresponding sloped length. For a uniform roof plane, it can also be used to convert horizontal footprint area into approximate sloped surface area. A 6:12 pitch has a factor of approximately 1.118.
Why is 4:12 an important roof slope?
OSHA defines a low-slope roof as having a slope less than or equal to 4:12 and a steep roof as greater than 4:12 for applicable workplace safety terminology. Roofing-product installation requirements are separate and should be checked for the specific product and project.
Can I measure roof pitch without climbing onto the roof?
Often, yes. Pitch may already appear on plans, or measurements may sometimes be taken from safely accessible framing or a clear gable reference. Complex or inaccessible roofs may be better measured by a qualified professional or measurement service.
Does a steeper roof have more surface area?
Yes, when the horizontal footprint remains the same. As roof pitch increases, the sloped surface gets longer, so the pitch factor increases. That is why roof-area calculations should account for slope.
Can one roof pitch represent the whole roof?
Sometimes, but not always. A simple roof may have one dominant pitch, while dormers, porches, garages, additions, or other roof sections can have different slopes. Complex roofs should be measured by roof plane when greater accuracy is needed.
Transparent math, clear limitations.
Pitch conversions use standard right-triangle trigonometry: rise divided by run, inverse tangent for angle, and the Pythagorean relationship for the pitch factor.
OSHA roof-slope terminology is used only where explicitly identified as workplace safety terminology. Roofing-material suitability, underlayment, installation details, and local requirements should be verified for the specific project and product.
Last reviewed: August 24, 2026
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