Roofing Calculators

Three calculators for the numbers that come up before a roofing job: how big the roof actually is, how steep it is, and how much material that adds up to. Each one runs entirely in your browser. Nothing you type is sent anywhere, stored, or seen by us.

  • Roof Area Calculator

    Turn a building footprint and a roof pitch into the actual roof area, in square feet and in roofing squares.

  • Roof Pitch Calculator

    Convert between rise over run, degrees and slope percentage, and see what the pitch means for materials and access.

  • Shingle Bundle Calculator

    Work out bundles, starter strip, hip and ridge cap, underlayment, drip edge and nails from your roof area.

  • Attic Ventilation Calculator

    How much net free ventilating area an attic needs, split between intake and exhaust, and what that is in vents.

  • Ice Barrier Coverage Calculator

    How far up the roof the ice and water membrane has to reach to clear the wall line, and how many courses that takes.

What these are for

They are for reading an estimate, not for replacing one. A roofer measures a roof plane by plane, allows for the way a particular product cuts around your particular valleys, and prices the access separately. These calculators use the standard methods that sit behind those figures, which is enough to tell a sensible number from a strange one.

That is the useful thing to be able to do. If two estimates for the same roof differ by forty per cent, the difference is usually in the assumptions rather than the arithmetic, and knowing roughly how much roof you have makes it possible to ask which assumption changed.

Start with the pitch

Almost everything else depends on it. Pitch sets how much larger the sloped surface is than the ground it covers, decides whether shingles are permitted on the roof at all, and determines whether a roofer can walk it or has to stage it. If you only measure one thing, measure that, and measure it from inside the attic rather than from the roof.

A note on units

The area and quantity calculators start in feet and switch to metres with one control. Roofing squares stay roofing squares in both: a square is 100 square feet wherever you are, because that is the unit materials are sold in.