Roofing Calculator
for Squares and Bundles
Enter the footprint and pitch of the roof. Get your squares, shingle bundles, underlayment rolls and nails, with waste included.
Pitch included · Waste included · Works on your phone
Estimates only. Your numbers stay in your browser and aren't saved or sent anywhere.
How to calculate roofing squares
A roofing square is 100 square feet of roof. To get there from the ground, you need the footprint and the pitch:
Sloped area = footprint × pitch factor
Squares = sloped area × (1 + waste %) ÷ 100
Bundles = squares × 3, rounded up
For example, a 40' by 30' footprint is 1,200 sq ft. At a 6:12 pitch, that's 1,344 sq ft of roof. Add 10% for waste and you need 14.78 squares, or 45 bundles of shingles.
Measure the footprint to the outside of the overhangs, not the walls, or you'll come up short.
Roof pitch multiplier chart
The factors the calculator uses, rounded up slightly from the exact multipliers:
| Pitch | Factor |
|---|---|
| Up to 2:12 | 1.02 |
| 3:12 | 1.04 |
| 4:12 | 1.06 |
| 5:12 | 1.08 |
| 6:12 | 1.12 |
| 7:12 | 1.16 |
| 8:12 | 1.20 |
| 9:12 | 1.25 |
| 10:12 | 1.30 |
| 12:12 | 1.41 |
How much waste to allow
About 10% suits a simple gable roof. Roofs with hips, valleys and dormers need more, often 15% or higher, because of the extra cuts.
What this leaves out
The calculator covers the main field of the roof. You'll still need to add ridge cap, starter strip, drip edge, flashing, and ice and water shield. It also assumes 3 bundles to the square, which is standard for most 3-tab and architectural shingles, but some heavier shingles take 4, so check the wrapper. Each slope of a roof with different pitches should be worked out separately.
Questions
- Most 3-tab and architectural shingles take 3 bundles per square, which covers 100 sq ft. Some heavier designer shingles take 4 or more, so check the wrapper.
- Put a level on the roof, measure 12" along it, then measure straight up to the roof surface. If that distance is 6", the pitch is 6:12.
- It depends on the type. A roll of 15 lb felt covers about 4 squares, 30 lb felt about 2, and synthetic about 10. Check the roll, because sizes vary.
- The squares will be right, but bundles and nails won't apply. Metal is ordered by panel length, so use the squares as your starting point and measure each slope.
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