Use this Roof Pitch Calculator to convert roof rise and run into pitch, angle, percent slope and slope factor. You can also start with an x:12 pitch, roof angle or percent slope and convert between formats using a visual roof-geometry diagram.
Enter the roof slope you know
Use rise/run measurements, an x:12 pitch, an angle, or percent slope. The calculator converts the same roof plane between all four descriptions.
Your roof pitch
Review pitch notation, angle, percent slope and the multiplier used for sloped lengths or areas.
Transparent calculation
How roof pitch is calculated
Roof rise and horizontal run form a right triangle. Every output below describes the same slope in a different format.
(rise ÷ run) × 12atan(rise ÷ run)(rise ÷ run) × 100√(1 + (rise ÷ run)²)√(12² + pitch rise²)rise ÷ run : 1Important: the calculator converts roof geometry only. Verify roofing-system limits, structural design and requirements that apply to the actual project separately.
Step-by-step
How to use the Roof Pitch Calculator
Choose the input that matches the information you already have. The calculator converts each input mode to the same underlying rise-to-run ratio, then displays the equivalent pitch, angle, percent slope and slope factor.
- Rise & run: enter a vertical rise and matching horizontal run measured in the same units.
- Pitch x:12: enter the roof's rise for every 12 units of horizontal run, such as 6 for a 6:12 pitch.
- Angle: enter the slope angle above horizontal when that value is already known.
- Percent: enter percent slope when plans, civil information or another source describes the roof that way.
- Calculate, then use the diagram and converted values to check that you entered the intended slope.
If you are measuring an existing roof, read How to Measure Roof Pitch before relying on one measurement.
Read your result
What each roof pitch result means
Pitch
The rise normalized to 12 units of horizontal run. A 6:12 pitch rises 6 units for every 12 units of run.
Roof angle
The angle between the roof plane and horizontal, calculated with right-triangle trigonometry.
Percent slope
The rise/run ratio multiplied by 100. A 6:12 pitch is a 50% slope.
Rise : run ratio
The unitless slope ratio before it is converted to x:12 pitch notation.
Slope factor
The multiplier that converts horizontal run or projected area to sloped length or sloped area for a simple planar roof surface.
Sloped length per 12 run
The hypotenuse associated with 12 units of horizontal run. It is useful for checking the roof's geometric multiplier.
Worked example
Example: convert a 6:12 roof pitch
A 6:12 roof rises 6 in for every 12 in of horizontal run. The rise/run ratio is 0.5.
6 ÷ 12 = 0.5atan(0.5) ≈ 26.565°0.5 × 100 = 50%√(1 + 0.5²) ≈ 1.118The sloped length over a 12 in horizontal run is approximately 13.42 in. Use the calculator above for the dimensions or slope description from your own project.
Measure carefully
Roof pitch measurement tips
- Rise and run must describe the same right triangle and use the same measurement units.
- For x:12 notation, the 12 represents horizontal run—not distance along the roof surface.
- Measure from plans, framing, an attic or another safely accessible location when possible rather than taking unnecessary fall risks.
- Check more than one location on older roofs because framing, settlement or additions can create different slopes.
- Do not confuse roof pitch with total roof height, rafter length or roof area; those require additional dimensions.
Know the limits
Assumptions and limitations
The Roof Pitch Calculator models a single straight roof plane using right-triangle geometry. It does not calculate valleys, hips, dormers, curved roofs, roof loading, member sizing, drainage design, flashing or structural connections.
The slope factor is a geometric multiplier. Applying it to an entire roof assumes the projected plan area corresponds to the same uniform slope. Complex roofs should be separated into simpler planes and measured individually.
Roofing products can have minimum or maximum slope requirements, special underlayment rules and manufacturer-specific installation limits. A geometric pitch result does not confirm that a particular roofing system is appropriate.
Terminology
Roof pitch, roof slope and roof angle are related but not identical labels
In everyday construction language, pitch and slope are often used interchangeably. BuildCalcForge keeps the outputs explicit: x:12 notation reports rise per 12 units of run, percent slope reports rise/run × 100, and angle reports the same relationship in degrees.
See Roof Pitch vs Roof Slope for a more detailed explanation of the terminology.
Common questions
Roof Pitch Calculator FAQ
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, feet, millimeters or another consistent unit because pitch is a ratio.
What angle is a 6:12 roof?
A 6:12 pitch corresponds to an angle of approximately 26.565 degrees above horizontal.
Is a 50% slope the same as a 6:12 pitch?
Yes. Six divided by twelve equals 0.5, and 0.5 multiplied by 100 is a 50% slope.
Can I calculate pitch from an angle?
Yes. The calculator converts the tangent of the angle to a rise/run ratio and then normalizes that ratio to x:12 pitch notation.
Does roof pitch tell me how many shingles I need?
Not by itself. Shingle quantity requires roof surface area plus waste and product-packaging assumptions. Use the Shingle Calculator after the roof geometry is known.
Does this calculator check roofing-code or manufacturer requirements?
No. It reports geometry. Verify minimum slope, underlayment, structural and installation requirements for the actual roofing system and jurisdiction.
Helpful guides
Learn the measurements behind the result
Sources & methodology
How this page is checked
The conversions use standard right-triangle geometry: tangent for angle, rise/run for ratio and percent slope, and the Pythagorean theorem for sloped length. BuildCalcForge shows the formulas and separates geometric results from product, code and structural decisions.