Roofing Calculator
Roof Parameters
Calculation Results
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How to Calculate Roofing Materials
- Roof area. Length × width of the footprint (including overhangs) × the pitch factor √(1 + (rise ÷ run)²). A 6:12 roof adds about 12%, an 8:12 roof about 20%, a 12:12 roof about 41%.
- Squares. Roofing is sold by the square: 100 sq ft of roof. Squares = roof area ÷ 100.
- Shingle bundles. Most asphalt shingles come 3 bundles to a square (one bundle covers about 33 sq ft). Bundles = squares × 3, then the waste factor. For a shingle-only estimate, use the roof shingle calculator.
- Waste. Cutting at edges, hips and valleys wastes material. The calculator uses 10% for gable and flat roofs and 15% for hip and mansard roofs, and shows the % it used.
- Underlayment, ridge cap and drip edge. Underlayment rolls = area × 1.1 ÷ 400 sq ft per roll; drip edge = perimeter + 10%. Ridge cap = roof length + 10% on gable roofs. On hip roofs the calculator shows a ridge & hip cap figure: the main ridge (length − width, 0 for a square roof) plus the four hips, each √(2 × (width ÷ 2)² + rise²), + 10%.
For metal, tile and slate the result is squares to order (with waste) instead of bundles.
Roofing Calculator Examples
Example 1: Gable roof, asphalt shingles
40 × 30 ft, 6:12 pitch, gable, asphalt
- Roof area: 1,341.64 sq ft = 13.4 squares
- Shingle bundles: 41 before waste, 45 with 10% waste
- Underlayment: 4 rolls · Ridge cap: 44 ft · Drip edge: 154 ft
- By hand: sheathing 47 sheets of 4 × 8 ft (area ÷ 32 + 10%); nails about 3,500-4,300 (about 260-320 per square, 4 per shingle)
Example 2: Steeper hip roof
40 × 30 ft, 8:12, hip, asphalt
- Roof area: 1,442.22 sq ft = 14.4 squares
- Bundles: 44 before waste, 50 with 15% waste
- Underlayment: 4 rolls · Ridge & hip cap: 115 ft · Drip edge: 154 ft
Example 3: Metal roof by the square
50 × 40 ft, 35°, hip, metal
- Roof area: 2,441.55 sq ft = 24.4 squares
- 29 squares to order with 15% waste
- Underlayment: 7 rolls · Ridge & hip cap: 150 ft · Drip edge: 198 ft
Example 4: Metric measurements
12 × 9 m, 30°, gable, asphalt
- Roof area: 1,342.34 sq ft (124.7 m²) = 13.4 squares
- Bundles: 41 before waste, 45 with 10% waste
- Underlayment: 4 rolls · Ridge cap: 44 ft · Drip edge: 152 ft
How Much Does a New Roof Cost per Square?
| Material | Installed per square (100 sq ft) | Per sq ft |
|---|---|---|
| 3-tab asphalt shingles | $300-$500 | $3-$5 |
| Architectural shingles | $400-$600 | $4-$6 |
| Metal (corrugated to standing seam) | $500-$1,600 | $5-$16 |
- Asphalt shingle bundles: $27-$45 (3-tab), $33-$85 (architectural).
- Labor for asphalt shingles: $2-$3 per sq ft ($200-$300 per square), usually 50-70% of the job.
Sources: HomeGuide, "Roofing Shingles Cost", updated November 2025; HomeGuide, "Metal Roof Cost", updated November 2025.
Example 1 above (13.4 squares) at $400-$600 per square: about $5,400-$8,000 for architectural shingles, before tear-off.
Roofing Materials Checklist
- Shingles: squares × 3 bundles (some heavy designer shingles are 4 bundles per square; check the wrapper).
- Starter strip along eaves and rakes, and hip & ridge cap shingles by the linear foot.
- Underlayment: synthetic or felt. Roll coverage varies by product (check the label); the calculator assumes 400 sq ft of coverage per roll.
- Ice and water shield at eaves and valleys where code requires it.
- Drip edge around the perimeter, flashing at walls, chimneys and valleys.
- Nails: 4 per shingle (6 in high-wind zones): about 260-320 per square (architectural shingles are fewer per square than 3-tab), or about 390-480 with 6 nails (GAF installation guidance).
- Sheathing if the deck is replaced: 4 × 8 ft sheets cover 32 sq ft each; add about 10%.
- Ventilation: ridge vent and soffit intake.
Waste factor: 10% for simple gable roofs, 15% for hips, and more for many valleys and dormers (HomeGuide: add 10-15%).