Free Online Roof Pitch Converter
Convert roof pitch between rise/run, degrees, and multipliers.
The span is the full width of the building. The rafter example uses half the span as its run.
All equivalents
The rafter length is a straight-line estimate for a simple gable and excludes the overhang, ridge board thickness, and birdsmouth cuts. Always add the overhang and a cutting allowance before ordering lumber.
About the Roof Pitch Converter
Roof pitch describes how steeply a roof rises. Builders, architects, and material estimators describe the same slope in several different ways, which is why conversions go wrong on job sites. A roof might be called 6:12, 26.6 degrees, a 50 percent slope, or a multiplier of 1.118. This converter accepts any one of those forms and fills in the rest, so a drawing, a supplier form, and a calculator can agree.
The four common notations
Rise over run is the traditional carpenter's notation: a 6:12 roof rises 6 units for every 12 units of horizontal run. Degrees measure the angle from horizontal, which is common in architectural drawings and solar work. Slope percentage is the rise divided by the run times one hundred; a 6:12 roof is 50 percent. The pitch multiplier is the factor you multiply by the run to get the sloped length, equal to the square root of one plus the pitch squared. For 6:12 it is about 1.118, so a 15-foot run has a rafter length of about 16.77 feet before allowances.
Why the multiplier matters
Roofing material quantities are based on the sloped area, not the flat footprint. If you know the horizontal run and the pitch, multiplying the run by the pitch multiplier gives the sloping length. Multiply that by the roof length and you have the area of one roof plane. Repeat for each plane, then add waste. The same factor helps estimate fascia, ridge, and underlayment, though each material has its own overlap and waste rules.
Span, run, and the example rafter
Span is the full width of the building, while run is the horizontal distance from the ridge to the wall, which is half the span for a symmetrical gable. This calculator uses half the span as the run for the example rafter. It does not include the overhang, so add the eave projection to the run before using the multiplier if you need the full rafter length. A ridge board also consumes a small amount of length at the top, and the birdsmouth cut removes material at the wall plate.
Frequently asked questions
What is a 4:12 pitch in degrees?
A 4:12 pitch has a rise of 4 units per 12 units of run. The angle is the arctangent of 4 divided by 12, which is about 18.4 degrees. The slope is 33.3 percent and the multiplier is about 1.054.
Is pitch the same as slope?
In roofing, pitch and slope are often used interchangeably, but strictly speaking slope is the ratio of rise to run and pitch is sometimes expressed as a ratio such as 6:12. This tool treats them as the same underlying ratio and shows both the x:12 form and the percentage.
How do I use the multiplier to order shingles?
Multiply the building footprint area by the pitch multiplier to approximate the sloped roof area, then add the overhangs and a waste allowance. For a complex roof, measure each plane separately; the multiplier is only a shortcut for simple rectangular planes.