Why measurements matter
A square is 100 square feet of roof surface. Because a sloped roof covers more area than the footprint beneath it, the pitch multiplier converts flat area to surface area. A steeper roof, a more complex shape and a larger overhang all add squares. Small errors in each compound quickly.
Ice and water shield
In cold climates, a self-adhering membrane is commonly installed along the eaves to help resist ice dam leaks. Local codes and manufacturers set how far up the roof it should extend. The calculator estimates two courses at the eaves; your roofer may recommend more, including valleys and penetrations.
Steep roofs
Snow-country roofs are often steep. Estimating software typically adds steep charges above certain pitches, and high roofs may add more. Check whether your estimate includes them.
Questions about this tool
Should I use the calculator instead of measuring?
No. It is a cross-check. An on-site measurement or aerial report is more accurate.
Why does waste change by roof type?
Hips, valleys and dormers require more cutting, so more material is wasted.