This roofing calculator converts your roof’s footprint and pitch into the numbers shingles are actually sold by: true roof area, roofing squares, and bundles — including a waste allowance.
Footprint should include eave overhangs (measure the roof outline from the ground plus overhang on each side). Complex roofs: calculate each section separately and add. Underlayment rolls typically cover ~4 squares each — divide your square count by 4 and round up.
Squares, Bundles and Pitch — Roofing’s Vocabulary
Shingles are sold by the square (100 sq ft of coverage) and packaged in bundles (typically 3 bundles = 1 square for standard shingles). The subtle part is area: the roof you shingle is the slope surface, larger than the house footprint underneath it. The pitch multiplier corrects for that: a 6/12 roof’s surface is √(1 + (6/12)²) = 1.118 times its footprint. This calculator is part of our Construction Calculators collection.
Worked Example (Verified)
A 40 × 30 ft footprint (1,200 sq ft) with a 6/12 pitch:
- True roof area: 1,200 × 1.118 = 1,342 sq ft
- Squares: 13.42
- Bundles: 13.42 × 3 ≈ 41, and with 10% waste ≈ 45 bundles
Pitch Multipliers
| Pitch | Angle | Multiplier |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Finding your pitch: in the attic or at a gable end, mark 12 horizontal inches on a level, then measure vertically up to the rafter — that vertical number is the rise in “X/12.”
Ordering Wisdom
- Waste: 10% covers simple gable roofs; hips, valleys and dormers push real roofs to 12–15%. Ridge cap shingles and starter strips are separate line items.
- Never measure from the house’s inside dimensions — the footprint must include overhangs, and wall thickness matters too. Satellite-measurement services exist precisely because roof geometry is underestimated from the ground.
- Underlayment and ice shield: roughly one roll per 4 squares for felt/synthetic; ice-and-water shield goes on eaves and valleys by local code.
- Safety: roof work is fall-risk work. Estimates are free to make from the ground — the arithmetic above is exactly how the pros start.
Related Tools
- Construction Calculators — the full collection
- Square Footage Calculator
Frequently Asked Questions
What is a roofing square?
100 square feet of roof coverage. A 2,000 sq ft roof surface is 20 squares — the unit for shingles, underlayment and labor pricing.
How many bundles of shingles do I need?
About 3 bundles per square for standard architectural shingles (some heavyweight products need 4–5 — check the bundle’s stated coverage). This calculator assumes 3 and adds your waste allowance.
How do I find my roof’s pitch?
Measure rise over a 12-inch horizontal run at a gable end or in the attic. A level and tape are all it takes — no roof walking needed.
Does the calculator handle hip roofs and dormers?
It handles any single section. For complex roofs, compute each plane with its own footprint and pitch, then add the bundles — and use a 12–15% waste allowance.
How much underlayment do I need?
About one roll per 4 squares for standard synthetic underlayment (coverage varies by product — check the roll label), plus ice-and-water shield for eaves and valleys.
Is this roofing calculator free?
Yes — free, instant, no sign-up. For a binding quote, a roofer’s on-site or satellite measurement still rules.