Roofing Calculator
Roof area from building size, overhang and pitch for gable, hip or shed roofs — squares, shingles, underlayment, drip edge, ice shield and ridge cap.
Your estimate
16.53 squares
Roofing squares (incl. waste)
- Actual roof area
- 1,503 sq ft
- Shingle bundles (10% waste)
- 50
- Pitch
- 6/12 · 26.6° · factor 1.12
- Eaves / rakes
- 84 ft / 72 ft
- Ridge / hips
- 42 ft / 0 ft
- Rafter length (incl. overhang)
- 17.89 ft
Show the math
- Plan area with overhangs = (L + 2 × overhang) × (W + 2 × overhang) = 1,344 sq ft
- × pitch factor √(1 + (6 ÷ 12)²) = 1.12 → roof area 1,503 sq ft
- × (1 + 10%) ÷ 100 sq ft = 16.53 squares → × 3 = 50 bundles
- Gable: two eaves, four rake edges, one ridge
Shopping list & cost
| Item | Spec | Qty | Cost |
|---|---|---|---|
| Asphalt shingles | 3 bundles per square | 50 bundles | — |
| Starter strip | 156 ft of eaves + rakes | 2 bundle(s) | — |
| Hip & ridge cap | 42 ft of ridge + hips | 2 bundle(s) | — |
| Synthetic underlayment | ~929 sq ft net per roll (3 in laps) | 2 roll(s) | — |
| Drip edge | 10 ft pieces, eaves + rakes | 17 | — |
| Ice & water shield | 36 in × 66.7 ft roll (200 sq ft) | 2 roll(s) | — |
| Roofing nails | 1¼ in coil, ≈ 320 per square (4 per shingle) | ≈ 5,290 | — |
Prices are what you enter under Advanced options. Estimates only — check stock and pricing with your supplier.
Quick answer A 40 × 30 ft house with 1 ft overhangs and a 6/12 gable roof has 1,503 sq ft of roof — 16.53 squares with 10% waste, or 50 bundles of shingles, plus 17 pieces of drip edge and 2 rolls of synthetic underlayment. A 12 × 9 m house at 6/12 needs 16.01 squares. Roof area = (L + 2 × overhang) × (W + 2 × overhang) × √(1 + (pitch ÷ 12)²).
Method & assumptions
Plan area = (L + 2 × overhang) × (W + 2 × overhang) Roof area = Plan area × √(1 + (pitch ÷ 12)²) Squares = Roof area × (1 + waste %) ÷ 100 Gable edges: eaves = 2 × L′, rakes = 4 × rafter, ridge = L′ Hip: eaves = perimeter, ridge = L′ − W′, 4 hips of √(2 × (W′/2)² + rise²)
- L′, W′
- building length and width including overhangs
- Pitch
- rise in inches per 12 in of run
- Square
- 100 sq ft of roof surface
Assumptions & limits
- A rectangular building with every roof plane at the same pitch.
- Dormers, valleys and cross-gables add area and waste — add them as separate sections or raise the waste factor.
- Shingles at 3 bundles per square; starter ≈ 105 ft and hip & ridge ≈ 33 ft per bundle; check your product.
- Roof work is dangerous. Measure from the ground or plans where possible and use fall protection.
Rounding: purchase quantities are always rounded up to whole units as sold. See our methodology.
Diagram
How to use this calculator
- Measure the building length (along the ridge) and width, wall to wall.
- Measure the overhang at the eaves and rakes — often 12–24 in.
- Enter the pitch. If you don't know it, measure the rise over 12 in of run with a level, or use the roof pitch calculator.
- Choose gable, hip or shed. Hip roofs use the same area formula but more waste and cap.
- Under Advanced, set ice & water shield courses for your climate and whether you are replacing the roof deck.
Worked examples
Imperial: 48 × 28 ft ranch, 18 in overhangs, 4/12 hip roof
- Plan = 51 × 31 = 1,581 sq ft × 1.054 = 1,667 sq ft
- +15% = 1,917 sq ft = 19.17 squares → 58 bundles
- Ridge = 51 − 31 = 20 ft; 4 hips × 22.5 ft = 90 ft of cap
Metric: 10 × 7 m garage, 0.4 m overhang, 30° (6.93/12) gable
- Plan = 10.8 × 7.8 = 84.2 m² × 1.155 = 97.3 m²
- +10% = 107 m² ≈ 11.5 squares → 35 bundles
- Eaves 21.6 m, rakes 4 × 4.5 m = 18 m → 14 drip edge pieces
In depth: roofing planning notes
From footprint to roof area
The flat area you can measure on the ground is not the roof area. Add the overhangs on all sides first — a 1 ft overhang on a 40 × 30 ft house adds 144 sq ft of plan area — then multiply by the pitch factor to account for the slope. Because every plane of a gable or hip roof with one pitch has the same slope, the same factor works for both styles: a hip roof over the same footprint has the same area as a gable, just arranged as four planes instead of two. What changes is the edge lengths and the waste: hips mean angled cuts along every hip line and more ridge cap.
For irregular houses, split the roof into rectangles, calculate each one with its own pitch, and add them. Dormers add their own small roofs and remove a little from the main one; valleys add waste and need valley lining. Many roofers simply add 5% to the waste factor for each significant complication. If you can get the building plans or an aerial measurement report, use them to cross-check the result.
The rest of the materials list
Shingles are only part of a roof. Synthetic underlayment covers the whole deck; a typical 10-square roll (42 in × 286 ft) nets about 929 sq ft once 3 in laps are taken off, so the calculator divides the roof area by 929 rather than 1,000. Where ice dams are a risk, the IRC requires an ice barrier from the eave to at least 24 in inside the exterior wall — one 36 in course on a short overhang, two on wide eaves or shallow pitches. Drip edge runs along every eave and rake. Starter strip goes along the eaves (and often the rakes), and hip and ridge cap covers the ridge and every hip.
If the deck is damaged or the old roof has too many layers, plan for new sheathing: 4 × 8 ft OSB or plywood sheets cover 32 sq ft each, and the calculator adds 5% for cuts. Vents, pipe boots, step flashing at walls and chimney flashing are counted on site. Order shingles from one lot so the color matches, and plan for disposal: a single layer of asphalt shingles weighs roughly 250–350 lb per square.
Reference table
| Material | Coverage |
|---|---|
| Asphalt shingles | 3 bundles = 1 square (100 sq ft) |
| Synthetic underlayment | ≈ 10-square roll (42 in × 286 ft) = 929 sq ft net with 3 in laps |
| Ice & water shield | 36 in × 66.7 ft = 200 sq ft per roll |
| Drip edge | 10 ft pieces, eaves and rakes |
| OSB / plywood deck | 4 × 8 ft = 32 sq ft per sheet |
Key facts
- 6/12 pitch factor
- 1.118 (12% more than plan area)
- Waste
- gable 10% · hip 15% · complex 20%
- Shingles minimum pitch
- 2/12; 2/12–4/12 needs double underlayment
Tips & common mistakes
- Order shingles from one production lot so the color matches across the roof.
- Drip edge goes under the underlayment at the eaves and over it at the rakes.
- Plan disposal: a tear-off of one layer of asphalt shingles weighs roughly 250–350 lb per square.
- If you're only checking a contractor quote, compare squares — most quotes are priced per square installed.
Frequently asked questions
How do I calculate roof square footage?
Multiply the building length and width including overhangs, then multiply by the pitch factor √(1 + (pitch ÷ 12)²). A 6/12 roof over a 42 × 32 ft plan is 1,344 × 1.118 = 1,503 sq ft.
How many squares is a 2,000 sq ft house roof?
For a single-story 2,000 sq ft house with 1 ft overhangs and a 6/12 roof, roughly 24–25 squares before waste and 27 with 10% extra. Two-story houses have about half the roof for the same floor area.
How many bundles of shingles do I need for 1,500 sq ft of roof?
1,500 sq ft is 15 squares; with 10% waste, 16.5 squares × 3 = 50 bundles.
Do I need drip edge?
Yes for asphalt shingle roofs under the IRC (R905.2.8.5): drip edge is required at eaves and rake edges.
How much ice and water shield do I need?
Where required, ice barrier must run from the eave to at least 24 in inside the exterior wall line (IRC R905.1.2) — one 36 in course on a short overhang, two on deeper eaves or low pitches.
Sources
- Owens Corning – Section 07 31 13 asphalt shingle guide specification (PDF) — accessed : “TruDefinition® Duration® Shingles: … Exposure: 5-5/8 in. Shingles per Square: 64. Bundles per Square: 3 bundles of 20 or 22 shingles. Coverage per Square: 98.4 sq ft (9.1 sq m).”
- Owens Corning – Starter Strip Plus data sheet (PDF) — accessed : “16 shingles per bundle, 105 lineal feet.”
- Owens Corning – ProEdge Hip & Ridge data sheet (PDF) — accessed : “Lineal Coverage per Bundle: 33 ft.”
- Owens Corning – ProArmor synthetic underlayment data sheet (PDF) — accessed : “Length per Roll 286 ft. · Width per Roll 42 in. · Coverage (with 3-in. overlap) 929 sq. ft.”
- Seattle Residential Code 2018 (IRC-based), Chapter 9 Roof Assemblies (PDF) — accessed : “R905.2.2 Slope. Asphalt shingles shall be used only on roof slopes of two units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from two units vertical in 12 units horizontal (17-percent slope) up to four units vertical in 12 units horizontal (33-percent slope), double underlayment application is required”
- GAF – shingle installation instructions and coverage — general reference — not cited for a specific figure
- NRCA – National Roofing Contractors Association — general reference — not cited for a specific figure
Default values (yields, coverage rates and densities) are typical figures from manufacturer literature. Always check the label on the product you buy.
Related calculators
- Shingle CalculatorTurn a house footprint and roof pitch into roof area, roofing squares and shingle bundles, plus starter, ridge cap and underlayment.
- Roof Pitch CalculatorConvert rise and run or an angle into roof pitch (x/12), degrees, percent slope and the pitch factor — plus ridge height and rafter length.
- Siding CalculatorSiding squares for a house — walls plus gables, minus doors and windows — with vinyl boxes or fiber cement planks, J-channel, corners and starter.
Learn more in our guides
Method, waste and worked examples: Roof area, squares and waste.
Worked project examples
- Gable roof example — hypothetical quantities, not a client job.
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DIYCalcLab. “Roofing Calculator.” Oct 20, 2026. https://diycalclab.com/roofing/roofing-calculator/
Estimates only. Verify quantities with your supplier and local building codes. For structural, electrical or safety-critical work, consult a licensed professional. Full disclaimer.