Shingle Calculator
By Taro Schenker | Updated February 11, 2026
Quick Answer: To calculate shingles, multiply building Length (ft) x Width (ft) x Pitch Multiplier, divide by 100 for squares, then multiply by 3 for bundles. Pitch multipliers: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414. Weight per square: 3-tab 200 lbs, architectural 275 lbs, premium 350 lbs. Underlayment rolls cover 400 sq ft. Ridge cap bundles cover 25 linear ft. Plan 2.5 lbs of nails per square. Add 15% waste for gable roofs. A 30 x 40 ft gable roof at 6/12 pitch needs about 41 bundles of shingles.
Calculate how many bundles of shingles you need for your roof. Enter your building dimensions and roof pitch, or input a known roof area, and get a complete materials list including underlayment, ridge caps, roofing nails, total weight, and estimated cost.
How to Calculate Shingles
The formula for calculating the number of shingle bundles is:
- Measure the building footprint length and width in feet.
- Multiply length × width to get the footprint area.
- Multiply by the pitch multiplier for your roof slope (e.g., 1.118 for a 6/12 pitch).
- Divide by 100 to convert square feet to roofing squares.
- Add your waste factor (15% is standard).
- Multiply by 3 (bundles per square) and round up.
Shingle Types Compared
Quick reference for common shingle types, weights, costs, and expected lifespan:
| Type | Weight / Square | Cost / Bundle | Lifespan | Warranty |
|---|---|---|---|---|
| 3-Tab | 200 lbs | $25-30 | 15-20 years | 25 years |
| Architectural | 275 lbs | $30-40 | 25-30 years | Lifetime |
| Premium / Designer | 350 lbs | $45-65 | 30-50 years | Lifetime |
Understanding Roof Pitch
Roof pitch is expressed as a ratio of vertical rise to horizontal run. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. Steeper pitches require more shingles because the actual roof surface area is larger than the building footprint.
Common pitch multipliers used to convert footprint area to actual roof area:
| Pitch | Multiplier | Extra Area |
|---|---|---|
| 4/12 (low slope) | 1.054 | +5.4% |
| 6/12 (standard) | 1.118 | +11.8% |
| 8/12 (moderate) | 1.202 | +20.2% |
| 10/12 (steep) | 1.302 | +30.2% |
| 12/12 (very steep) | 1.414 | +41.4% |
Formula Summary
Roof Area Formula: Calculate the total roof surface area by multiplying the building footprint by the pitch multiplier.
$$A_{\text{roof}} = L_{\text{ft}} \times W_{\text{ft}} \times M_{\text{pitch}}$$
Bundles Formula: $$\text{Bundles} = \lceil \frac{A_{\text{roof}}}{100} \times (1 + W\%) \times 3 \rceil$$
Underlayment: $$\text{Rolls} = \lceil \frac{A_{\text{roof}}}{400} \rceil$$ Ridge Caps: $$\text{Bundles} = \lceil \frac{L_{\text{ridge}}}{25} \rceil$$
Nails: $$\text{Nails (lbs)} = \lceil \text{Adjusted Squares} \times 2.5 \rceil$$ Weight: $$W = \text{Adjusted Squares} \times \rho_{\text{shingle}}$$
| Shingle Type | Weight/Square (lbs) | Default Price/Bundle |
|---|---|---|
| 3-Tab | 200 | $28 |
| Architectural | 275 | $35 |
| Premium / Designer | 350 | $55 |
| Constant | Value |
|---|---|
| Underlayment per roll | 400 sq ft |
| Ridge cap per bundle | 25 linear ft |
| Nails per square | 2.5 lbs |
| Bundles per square | 3 |
Standard Assumptions: Waste factor of 15% for simple gable roofs. Hip roof ridge length = building length + width. Gable roof ridge length = building length. Pitch multiplier for 6/12 = 1.118 (most common residential pitch).
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- Roofing Calculator — estimate total roofing materials and labor costs
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- Insulation Calculator — estimate attic and roof insulation requirements
Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.