Roofing Calculator
This roofing calculator turns your roof's footprint (or a roof area you've already measured) and its pitch into squares, shingle bundles, and every underlayment and trim accessory — plus an installed-cost range and a tear-off dumpster estimate.
Price edits are remembered on this device — no account, nothing sent anywhere.
1.61 tons fits a 10–15-yard dumpster. Steep pitches (8/12+) add access labor most bids price separately.
Estimates only, not quotes. Prices are editable national averages — confirm current pricing and quantities with your supplier before you buy.
How this roofing calculator converts footprint to squares and bundles
Roofs are measured and priced in squares — 100 sq ft of actual sloped surface. Your house's footprint understates that surface because the roof tilts, so the calculator multiplies footprint by a pitch factor: the geometric ratio between a sloped run and its horizontal projection. A 6/12 roof carries factor 1.118; a steep 12/12 carries 1.414. If you've already measured true roof area (from plans or a satellite tool), enter it directly and the conversion is skipped.
Bundles follow at three per square, inflated by a waste percentage the complexity selector sets — 10% for a simple gable, 15% for a hip roof, 20% for a cut-up roof with dormers and valleys — since every extra cut angle throws away more of a bundle. Accessories are counted in the units stores sell: underlayment rolls by coverage, ice & water shield, drip edge, and starter strip by eave/rake length, ridge cap by ridge+hip length.
The installed range prices the whole job per square — labor, disposal, and materials — using editable low/high rates by shingle type, and the tear-off line converts old-roof debris to tons so you can size a dumpster before the first shingle comes off.
The formula
Worked example: bundles and cost for a 40×30 ft gable roof
Default inputs: a 40 ft × 30 ft footprint (1,200 sq ft), 6/12 pitch, simple gable (10% waste), architectural shingles, ridge+hip 40 ft, eave+rake 140 ft, one tear-off layer, all five accessories included.
- 1. Roof area1,200 × 1.118 = 1,342 sqft → 13.42 squares
- 2. Bundlesceil(13.42 × 3 × 1.10) = 45 × $42 = $1,890
- 3. Underlaymentceil(13.42 × 1.10 ÷ 10) = 2 rolls = $150
- 4. Ice & waterceil(140 ÷ 66) = 3 rolls = $345
- 5. Drip edgeceil(140 ÷ 10) = 14 sticks = $126
- 6. Starter stripceil(140 ÷ 110) = 2 rolls = $90
- 7. Ridge capceil(40 ÷ 30) = 2 bundles = $110
- 8. Materials subtotal$2,711
- 9. Installed range13.42 × $450–$700 = $6,037–$9,391
- 10. Tear-off debris13.42 × 1 × 240 ÷ 2000 = 1.61 tons
Switching to 3-tab shingles on the same roof drops the bundle price to $30 and the installed range to $350–$550/square: materials fall to $2,171 and the installed range becomes $4,696–$7,379.
Assumptions & defaults
| Pitch factors | 3/12 ×1.031 → 6/12 ×1.118 → 9/12 ×1.25 → 12/12 ×1.414 |
| Waste by complexity (editable) | Gable 10% · hip 15% · complex 20% |
| Bundles per square | 3 |
| Coverage rates | Underlayment 10 sq/roll · I&W 66 lf · drip 10 lf · starter 110 lf · ridge 30 lf |
| Tear-off debris | 240 lb per square per layer |
| Shingle defaults (editable) | Architectural $42/bundle, $450–700/sq · 3-tab $30, $350–550 |
Ridge/hip and eave/rake lengths default to a simple gable estimate (ridge = house length; eaves+rakes = 2 × (length + width)) and track your dimensions until you edit them — override both for hip or complex roofs. Every price is an editable national-average estimate, reviewed July 2026.
How much does a roof replacement cost per square?
A roofing cost calculator and a roofing quantity calculator answer the same question from two ends, and this page runs both: the installed-cost range in the results panel is your material list priced with labor, and dividing it by the squares line gives your roof's replacement cost per square. Complexity moves that number more than size — hips, valleys and dormers add cutting waste (the waste factors reference explains why a cut-up roof runs 15–20%), steep pitches add access labor, and tear-off layers add disposal tonnage the calculator already prints. If the roof tops a new outbuilding, the cost to build a garage calculator prices the whole structure around it.
Roof pitch multiplier chart
| Pitch | Multiplier | Angle |
|---|---|---|
| 4/12 | 1.054 | 18.4° |
| 5/12 | 1.083 | 22.6° |
| 6/12 | 1.118 | 26.6° |
| 7/12 | 1.158 | 30.3° |
| 8/12 | 1.202 | 33.7° |
| 9/12 | 1.250 | 36.9° |
| 10/12 | 1.302 | 39.8° |
| 12/12 | 1.414 | 45.0° |
The multiplier is √(1 + (rise/12)²) — pure trigonometry, so it never needs a price review. Footprint × multiplier = roof surface; skipping it under-orders a 12/12 roof by 41%, the costliest mistake in the takeoff method.
Sources & standards
The pitch-multiplier table is standard roofing-trade geometry (slope length ÷ run for each rise-over-12). Coverage rates for underlayment, ice & water shield, drip edge, starter strip, and ridge cap reflect manufacturer packaging and technical data sheets for widely stocked US products. Ice-barrier placement at eaves follows the 2021 IRC, section R905.1.2 in cold regions — verify the requirement with your local building department. Tear-off weight reflects published asphalt-shingle debris-weight figures used in dumpster sizing. Prices reviewed July 2026 — see how our price reviews work.