Roofing calculators & guides
Free roofing tools and plain-English guides for United States — each gives the answer fast and shows the working behind it.
Roof pitch calculator
Enter rise and run — get the pitch (x:12), the roof angle, grade %, slope factor and rafter length.
Open tool →Roofing calculator
How much roofing do I need? Enter your roof footprint and pitch — get the area, the roofing squares and how many bundles of shingles to order.
Open tool →About roofing calculations
Roofing math starts with pitch: the ratio of vertical rise to horizontal run that determines which materials are allowed on the roof, how it sheds water, how much surface area you're actually buying material for, and whether you can safely walk on it. The same right-triangle relationship gives you rafter lengths and the true area of a sloped surface — which is always more than the footprint it covers, a difference that ruins material estimates when it's forgotten.
The roofing tools here convert between pitch formats (ratio, degrees, percentage), calculate true roof areas from plan dimensions, and show the geometry behind every result. Inputs work in metric or imperial, because roofing specs routinely arrive in both on the same job.
Using the results
Pitch thresholds matter because manufacturers void warranties on materials installed below their minimum slope, and local rules often encode the same limits. Calculate here, then check the specific product's installation requirements and your local rules before ordering. And treat any roof — especially anything steeper than you'd happily stand on — as fall-protection territory; the math is the easy part of roofing.