Roofing Calculator (Squares, Shingle Bundles and Underlayment)

Shingles are sold by the bundle, three to a square (100 sq ft) for most products. This roofing calculator finds the roof surface from the building footprint and pitch, or takes the area you measured, then adds waste and converts it into bundles, underlayment rolls, hip-and-ridge bundles and an estimate of nails. Use the roof pitch calculator first if you only know the rise and run.

Roofing shingles calculator

How it works

Pitch factor = √(1 + (rise ÷ 12)²): 1.118 for 6/12, 1.202 for 8/12, 1.414 for 12/12
Roof area = footprint (including overhangs) × pitch factor
Squares = area ÷ 100, plus waste
Bundles = squares × bundles per square, rounded up (Owens Corning’s guide specification lists 3 bundles per square and 98.4 to 100 sq ft coverage for its standard shingles)
Underlayment = squares ÷ squares per roll, with 10% for laps

Worked example

A 40 × 30 ft gable roof (measured with the overhangs) at 6/12 pitch, 40 ft of ridge, 10% waste, synthetic underlayment:

Measure by: Building footprint and pitch
Building length (including overhangs): 40 ft
Building width (including overhangs): 30 ft
Roof pitch (rise per 12 in of run): 6
Waste: 10%
Bundles per square: 3
Ridge and hip length: 40 ft
Ridge cap coverage per bundle: 33 linear ft
Underlayment: Synthetic, 10 squares per roll

The calculator gives:

Shingle bundles: 45 (14.8 squares including 10% waste, at 3 per square)
Roof area: 1,342 sq ft = 13.42 squares (footprint × 1.118 pitch factor)
Hip and ridge cap: 2 bundles for 40 ft
Underlayment: 2 rolls (10 squares per roll, 10% overlap allowance)
Roofing nails: about 4,723 (4 per shingle, roughly 320 per square)

The footprint of 1,200 sq ft becomes 1,342 sq ft of roof surface, 13.4 squares. With 10% waste that is 14.8 squares, 45 bundles. Two rolls of synthetic underlayment, two bundles of ridge cap and about 4,700 nails (roughly 21 lb of 1-1/4 in roofing nails). Hips and valleys would push the waste to 15% and 50 bundles.

Notes and limits

Measure the footprint to the outside of the overhangs, not the walls. A 1 ft overhang all round adds about 10% to a 40 × 30 ft roof.
Bundles per square varies: some heavy laminated and designer shingles are 4, 5 or 6 bundles per square. Read the wrapper.
Starter strip along the eaves and rakes, drip edge, ice-and-water membrane in valleys and at eaves, flashing, pipe boots and ridge vent are extra.
Asphalt shingles need a minimum 2/12 slope, with double underlayment between 2/12 and 4/12 (IRC R905.2.2).
Tear-off and disposal of the old roof is often the biggest surprise cost.

Frequently asked questions

How many bundles of shingles do I need for 1,500 square feet?

15 squares plus 10% waste is 16.5 squares, so 50 bundles at 3 per square.

How many square feet does a bundle of shingles cover?

About 33 sq ft for standard three-bundle-per-square shingles (Owens Corning lists 98.4 to 100 sq ft per three bundles). Heavier shingles cover less per bundle.

How do I calculate roof area from the pitch?

Multiply the footprint by the pitch factor √(1 + (rise ÷ 12)²). A 6/12 roof is 1.118 times its footprint, an 8/12 roof 1.202.

How much waste for roofing shingles?

10% on a simple gable, 15% or more with hips, valleys and dormers.

How many roofing nails per square?

About 320: four per shingle and roughly 80 shingles per square. High-wind areas use six per shingle, so 480.

Sources

Last reviewed: 26 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.