Shingles Needed Calculator

Shingle quantity starts from the roof area, not the floor area. Steeper roofs cover more surface, so the pitch multiplier has to be applied before anything is ordered.

Roof lengthThe length of the roof at the eaves, in feet.Roof widthThe width of the roof at the eaves, in feet. For a gable this is half the span.Pitch riseInches of rise per twelve inches of run. A 6/12 pitch means 6.Waste allowance(%)A percentage for cuts, starter courses and ridge caps. Ten percent suits a simple roof.

Sloped roof area

1,341.64

Squares needed: 14.76
Bundles needed: 45
Underlayment rolls: 4
Pitch multiplier: 1.118

Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.

The formula this calculator uses

squares = roof length x roof width x pitch multiplier x (1 + waste) / 100

squares: Roofing area in units of 100 square feet
bundles: Three bundles make one square for standard shingles
pitch multiplier: The square root of one plus pitch over twelve squared
waste: An allowance for cuts, starter courses and ridge caps

How to check the result by hand

1
Measure the footprint
A 40 by 30 foot roof has a footprint of 1200 square feet. For a gable roof this is simply the length times the width at the eaves.
2
Apply the pitch multiplier
At 6/12 pitch the multiplier is the square root of one plus 0.25, which is 1.118. The sloped area is 1200 times 1.118, which is 1341.64 square feet.
3
Add the waste allowance
Ten percent waste brings 1341.64 to 1475.8 square feet. Complex roofs with valleys and dormers should use fifteen percent instead.
4
Convert to squares and bundles
1475.8 divided by 100 is 14.76 squares, and at three bundles per square that is 44.27 bundles, so order 45 bundles. Underlayment at 400 square feet per roll needs four rolls.

For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Shingles Needed page.