How to Calculate Shingles for a Roof
Roofing is measured in squares and sold in bundles. This guide explains how to turn your roof footprint and pitch into an accurate shingle order — with waste built in.
Ready to run the numbers? Use our Roofing Shingle Calculator or the Shingle Calculator to get an instant material estimate.
Measure the roof footprint
The footprint is the building length × width per roof plane, including overhangs — not the sloped surface area. For a simple gable, that is length × width. For a hip roof, measure each plane and add them. You can measure from the ground or from a ladder; you do not need to walk the roof.
Apply the pitch factor
A sloped roof has more surface area than the flat footprint below it. The pitch factor converts footprint to true surface area. Find your pitch (rise over run, in inches) and multiply the footprint by the factor.
- 4/12 pitch → ×1.054
- 6/12 pitch → ×1.118
- 8/12 pitch → ×1.202
- 10/12 pitch → ×1.302
- 12/12 pitch → ×1.414
Convert to squares and bundles
Roofing is measured in squares — one square covers 100 ft². Standard 3-tab and architectural shingles come 3 bundles per square. Multiply true surface area by your waste allowance, divide by 100 for squares, then by 3 for bundles.
Source: 1 square = 100 ft²; 3 bundles per square for standard asphalt shingles.
A 30×40 ft roof (1,200 ft²) at 6/12 pitch (×1.118) with 10% waste: 1,200 × 1.118 × 1.1 = 1,476 ft² = 14.8 squares × 3 = 45 bundles.
Waste and accessories
- 10% waste for a simple gable; 15% for hips, valleys, and dormers.
- Order matching starter strips, ridge cap shingles, and underlayment.
- Add drip edge, ice-and-water shield for valleys, and roofing nails.
- Steep roofs (12/12+) cost more in labor and need more waste.
Frequently asked questions
How many bundles of shingles are in a square?
Three bundles make one square (100 ft²) for standard 3-tab and architectural shingles. Some designer/luxury shingles require 4 or more bundles per square — check the bundle label.
How do I figure out my roof pitch?
Pitch is rise over run in inches per foot. From the ground or attic, measure the rise over a 12-in horizontal run. A 6-in rise over 12 in of run is a 6/12 pitch, with a surface factor of about 1.118.
How many bundles do I need for a 1,000 sq ft roof?
1,000 ft² of true roof surface is 10 squares, or 30 bundles of standard shingles. Add 10% waste for a simple gable, so order about 33 bundles.
Calculators for this guide
Put these numbers to work with the free calculators referenced above.