Roofing Material Calculator

Enter the roof's length and width as measured on the ground plan, choose the pitch, and the calculator applies the standard slope multiplier for that pitch to get the true sloped area. Roofing is sold by the 'square' — 100 sq ft of coverage — and this tool converts the area into squares, shingle bundles (3 bundles per square, the standard for most asphalt shingles) and rolls of underlayment at about 400 sq ft of coverage per roll.

Multipliers used: 0/12 = 1.000, 3/12 = 1.031, 4/12 = 1.054, 5/12 = 1.083, 6/12 = 1.118, 7/12 = 1.158, 8/12 = 1.202, 9/12 = 1.250, 10/12 = 1.302, 11/12 = 1.357, 12/12 = 1.414. Squares and rolls are rounded UP to whole purchasable units. Hips, valleys and starter/ridge courses add waste beyond this flat estimate — add a square for complex roofs.

The formula

Roof area = Length × Width × pitch multiplier; Squares = Area ÷ 100; Bundles = ceil(Squares) × 3; Rolls = ceil(Area ÷ 400)

Worked example

A 40 × 30 ft roof plan is 1,200 sq ft; at a 6/12 pitch (×1.118) the sloped area is 1,342 sq ft = 13.42 squares. Order 14 squares: 42 shingle bundles and 4 rolls of underlayment.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

How many bundles of shingles are in a square?

Three bundles for most standard architectural shingles — a square (100 sq ft) takes 3 bundles. Some heavyweight shingles come 4 or 5 bundles to the square; check the wrapper's coverage statement.

How accurate is measuring from the ground plan?

For a simple gable roof it is within a few percent once the pitch multiplier is applied, as long as you include the eave and rake overhangs in the length and width. Complex hip roofs with many valleys need section-by-section measurement.

How much extra should I order?

Add about 10% for a simple gable roof and 15% for hip roofs to cover cuts, hips, valleys, starter and ridge courses. This calculator's round-up to whole squares covers part of that.

Category: Construction & Home calculators

Flat (plan) area	1,200 sq ft
Sloped roof area	1,342 sq ft
Squares (exact)	13.42
Squares to order	14
Shingle bundles (3 per square)	42
Underlayment rolls	4