CategoriesRoofing

Roofing Calculators

Roofing calculators for shingles, underlayment, ridge caps, and material cost estimation. Calculate by pitch, type, and material.

6 Calculators

All roof types

Always Free

Roofing is measured in squares, and the pitch decides how much roof there is.

A roofing square is 100 square feet, and it is the unit everything is priced in. The catch is that roof area is not footprint area: a 6/12 pitch has about 12% more surface than the ground it covers, and a 12/12 pitch has 41% more. Measuring the house from above and forgetting the pitch multiplier is the most common way a roofing estimate comes in short.

Pitch also decides what you are allowed to install. Asphalt shingles need at least a 2/12 slope, and below 4/12 they need a double underlayment. Anything under 2/12 is a membrane roof, not a shingle roof, whatever the budget says.

Settle this before you calculate

Pitch, as a rise over 12: Measure 12 inches horizontally along a level and read the drop to the roof. That ratio drives both the area multiplier and the material choice.
Every plane, separately: Hips, valleys, dormers and porches are each their own rectangle or triangle. A complex roof measured as one shape is always wrong.
Linear feet of edges: Ridge, hip, valley and eave lengths drive ridge cap, flashing and drip edge, which are priced per foot rather than per square.

Where the estimate goes wrong

Ordering by footprint: Multiply by the pitch factor. A 2,000 square foot footprint at 8/12 is about 2,400 square feet of roof, or 24 squares before waste.
Forgetting waste on cuts: Add 10% on a simple gable and 15% or more where there are valleys and hips, because every valley course gets cut twice.
Reusing old flashing: Flashing is cheap and it is where roofs leak. Replace it with the roof rather than saving a small line item on a 25-year installation.