🛖 Roofing Calculator PRO
Professional roofing material estimator — shingles, underlayment, flashing, ventilation & more.
Dimension Diagram — updates as you type
Footprint × pitch gives the true sloped area. Overhang adds eave coverage beyond the walls.
1Roof Dimensions
Pitch factor: — covers ° from horizontal
Industry standard: 10% for simple roofs, 15% for complex. ⚠ Low waste may cause shortages.
2Shingle & Underlayment
Required by code in most cold climates — extends 24" past interior wall line.
3Material Pricing
4Project & Labour
Labour Cost
Results
Roof Geometry
Material Quantities
Ventilation
Cost Breakdown
⚠️ Pre-Export Checklist
- Building dimensions verified on-site
- Roof pitch confirmed (use a pitch gauge)
- Overhang distances measured and specified
- Local building code requirements checked (ice dam zone, wind uplift)
- Underlayment type selected for climate
- Flashing locations identified (chimneys, walls, valleys, pipes)
- Ventilation meets code (1/150 or 1/300 NFA ratio)
- Existing roof deck condition inspected
- Material pricing confirmed with supplier
Professional Roofing Estimation Guide
📐 Formulas & Calculations ▼
Pitch Factor
Pitch Factor = √(1 + (pitch/12)²)
| Pitch | Factor | Angle |
|---|---|---|
| 4:12 | 1.054 | 18.4° |
| 6:12 | 1.118 | 26.6° |
| 8:12 | 1.202 | 33.7° |
| 10:12 | 1.302 | 39.8° |
| 12:12 | 1.414 | 45.0° |
| 16:12 | 1.667 | 53.1° |
Roof Area
Gable:Area = (Length + 2×Overhang) × (Width + 2×Overhang) × Pitch Factor
Hip:Same base area × pitch factor, plus hip rafter length = Width/2 × pitch factor
Shed:Single slope: Length × (Width + Overhang) × Pitch Factor
Gambrel:Each side = (Length × Upper Width + Length × Lower Width) × respective pitch factors
Mansard:Perimeter × steep section height × steep pitch factor + top flat section
Shingle Coverage
1 Square = 100 sq ft of roof area
3-Tab: ~3 bundles/square (each covers ~33.3 sqft)
Architectural: ~3 bundles/square (each covers ~33.3 sqft, but thicker)
Luxury: ~2.5 bundles/square (each covers ~40 sqft)
Underlayment Coverage
15 lb felt: 4 squares per roll (432 sqft net)
30 lb felt: 2 squares per roll (216 sqft net)
Synthetic: 4 squares per roll (1000 sqft net)
Ice & Water Shield: 2 squares per roll (192 sqft net)
Ventilation (NFA)
Required NFA = Attic Floor Area ÷ 150 (or ÷ 300 with balanced intake/exhaust)
Ridge vent NFA = Linear Feet × Vent NFA per LF (typically 18 sqin/LF)
Attic Floor Area = Roof Deck Area × 0.5 (conservative estimate)
🔢 Worked Example ▼
30 ft × 20 ft Gable Roof, 6/12 Pitch, 2 ft Eave Overhang, 1 ft Rake Overhang:
- Adjusted length: 30 + 2×2 = 34 ft
- Adjusted width: 20 + 2×2 = 24 ft
- Pitch factor (6/12): √(1 + 0.5²) = 1.118
- Roof area: 34 × 24 × 1.118 = 913 sqft
- With 10% waste: 913 × 1.10 = 1,004 sqft
- Squares: 1004 ÷ 100 = 10.04 squares
- 3-tab bundles: 10.04 × 3 = 31 bundles
- Underlayment (30lb): 1004 ÷ 216 = 5 rolls
- Starter strips: (34 × 2) ÷ 33 = 3 bundles
- Ridge caps: 34 ÷ 3.3 = 11 bundles
- Drip edge: (34×2) + (24×2×1.118×2) = 175 LF
- Nails (4 nails/shingle): ~600 shingles × 4 = 2400 nails → 10 boxes
🚫 Common Mistakes to Avoid ▼
- Forgetting pitch factor — A 12:12 pitch adds 41% more area than flat measurement. Always multiply by the pitch factor.
- Ignoring overhangs — Eave and rake overhangs add 1-4 ft on each side. Measure from the fascia, not the wall.
- Under-ordering waste — Complex roofs (hips, valleys, dormers) need 15-20% waste. Simple gables can get by with 10%.
- Wrong nail count — 4 nails per shingle in normal wind, 6 in high-wind zones. Never use staples unless code allows.
- Skip ice & water shield — Required by code in most cold climates at eaves, valleys, and around penetrations. Don't skip it.
- Wrong exposure — 3-tab: 5" exposure. Architectural: 5.5" or per manufacturer. Incorrect exposure = leaks and warranty void.
- Ignoring ventilation — Undersized venting causes ice dams, mold, and premature shingle failure. Calculate NFA properly.
- Not checking the deck — Rotted or delaminated OSB/plywood must be replaced before shingling. Budget for deck repair.
💡 Pro Tips ▼
- Measure twice, order once. Walk the perimeter with a laser measurer. Verify pitch with a smartphone level app.
- Start from the bottom. Always install underlayment and shingles bottom-to-top for proper water shedding.
- Use chalk lines. Snap horizontal lines at exposure intervals for straight courses. Invest 10 minutes, save hours of rework.
- Bundle count safety margin: Order 1 extra bundle per 10 squares for future repairs. Colors can vary between production runs.
- Valley treatment: Closed-cut valleys are cheapest. Open metal valleys last longest. Woven valleys are obsolete.
- Ridge vent sizing: Balance intake (soffit) and exhaust (ridge). Aim for 60% intake, 40% exhaust minimum.
- Labour estimate: Experienced crew: 1 square/hour. DIY: 0.25-0.5 squares/hour. Include tear-off and disposal time.
- Warranty registration: Architectural shingles require proper underlayment and ventilation for manufacturer warranty. Document everything.
- Price shopping: Get 3 supplier quotes. Prices vary 15-30% between suppliers for identical products.
Drag to rotate — Scroll to zoom
حاسبات مرتبطة
Frequently used together on the same project.
Client & Quote (prints on PDF & Excel)
Adjustments (applies to exports)
Contingency is added as a separate line on the exported cost summary. Waste % is printed as an advisory reminder.
Project notes (prints on PDF & Excel)
Result compare (A/B)
| Item | Pinned | Current | Change |
|---|---|---|---|
Saved rates auto-apply from your Price Library. Advanced details stay in your browser — nothing is uploaded except inside your own PDF/Excel exports.
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❓ أشفاع مشهورة
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✅Method, Sources & Review
Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.