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Roof Pitch Calculator
Enter vertical rise and horizontal run in the same unit to calculate the slope of one roof section.
Basic Calculator
Perform basic math operations like addition, subtraction, multiplication, and division. Includes memory functions and square root support.
About the Roof Pitch Calculator
Roof pitch here means vertical rise per 12 units of horizontal run, written X:12. Run is the horizontal distance for the roof section being measured, not its sloping length. For a symmetric gable roof, one side usually has a run of half the full span; do not halve the run again if you already measured one side.
How to use it
Enter the vertical rise and horizontal run, select their shared unit, and calculate. Use decimals when needed. Rise may be zero to represent a flat slope; run must be positive. The rafter result uses the selected unit. Copy includes the inputs, results and geometric assumptions.
Formula / Explanation
Slope = rise / run. Pitch = 12 × slope, expressed as X:12. Angle = atan(slope) × 180 / π. Slope percentage = 100 × slope. Straight-line rafter length = √(rise² + run²). Both lengths are converted to meters internally using in × 0.0254, ft × 0.3048, cm × 0.01 or m × 1; the rafter result is converted back to your chosen unit.
Example
Rise 6 inches and run 12 inches give slope 0.5, pitch 6:12, angle approximately 26.56505118°, slope 50% and straight-line rafter length approximately 13.41640786 inches. Equivalently, rise 15.24 cm and run 30.48 cm give the same pitch and angle, with length approximately 34.07767598 cm.
Is run the same as the roof span?
No. Run is the horizontal distance covered by the measured sloping section. Full span may include two sides. Use the actual run for each section, especially on asymmetric roofs.
Does 6:12 mean an angle of 6 degrees?
No. It means 6 units of rise for every 12 units of run. That is a 50% slope and an angle of approximately 26.565 degrees. Pitch, angle and percentage express the same slope differently.
Can I mix feet and inches in the input fields?
No. Convert both measurements to the same unit first. For example, 1 foot 6 inches is 18 inches or 1.5 feet. Use the Unit Converter if needed.
Is the rafter length ready for cutting?
No. It is only the geometric length between the endpoints of the entered rise and run. It excludes overhangs, ridge thickness, birdsmouths, cut allowances and material requirements. It does not assess loads, structural safety, drainage, roofing suitability or building-code compliance.
Can I use zero rise or negative measurements?
Zero rise gives 0:12, 0 degrees and a rafter length equal to run. Negative measurements and zero run are rejected. Enter positive magnitudes for a downward slope; this calculator does not represent slope direction.
Does this calculate roof area or material quantities?
No. For simple geometric areas see the Area Calculator. Roof coverings, waste, overlaps and structural design require additional information.