Roofing Calculators

How roofing estimating works

Roofing is measured in squares — 100 sq ft of roof surface — and asphalt shingles are usually packaged three bundles to the square. The key step is converting the flat footprint you can measure on the ground into the sloped area of the roof, using the pitch factor √(1 + (rise ÷ 12)²). A 6/12 roof has about 12% more surface than its footprint; a 12/12 roof has 41% more.

Hips, valleys and dormers add cutting waste, which is why hip roofs typically need 15% extra rather than 10%. Roof work is dangerous: measure from plans or at the eaves where possible, and use fall protection or a professional.

Glossary

Square

100 sq ft (9.29 m²) of roof

Pitch

rise in inches per 12 in of run, e.g. 6/12

Starter strip

first course along the eaves

Ridge cap

shingles that cover hips and ridges

Updated 2026-10-18 by the DIYCalcLab Editorial Team · How we calculate