Roofing Calculator — Shingles, Underlayment & Materials Estimate
Calculate roofing squares, shingle bundles, underlayment rolls, drip edge, starter strip, ridge caps, and nails for any roof size and pitch.
How to Use This Calculator
- Enter your roof footprint dimensions (measured at the eaves, not along the slope)
- Select your roof pitch — use the Roof Pitch Calculator if unknown
- Choose your shingle type
- Enter ridge length and number of valleys if known
- Set the waste factor (15% is recommended for standard roofs)
- Click "Calculate Roofing Materials" for a complete estimate
How the Calculation Works
footprint_area = length × width
pitch_multiplier = sqrt(1 + (rise/12)²)
actual_roof_area = footprint_area × pitch_multiplier
roofing_squares = actual_roof_area / 100
bundles = roofing_squares × 3 // 3 bundles per square for shingles
underlayment_rolls = ceil(actual_roof_area / 400)
drip_edge_ft = (2 × width) + (2 × length × pitch_multiplier) // perimeter + ridge
starter_strip_ft = 2 × width + 2 × length // eaves and rake perimeter
ridge_cap_bundles = ceil(ridge_length / 33.3)
nails_lbs = roofing_squares × 2.5 The pitch multiplier converts your horizontal footprint to actual sloped roof area. Roofing is sold in "squares" (100 sq ft). Three bundles of architectural shingles cover one square. Underlayment rolls cover ~400 sq ft each. Drip edge runs along all perimeter edges. Starter strip goes along eaves. Ridge caps come at ~33 linear feet per bundle.
Variables:
- pitch_multiplier: Converts footprint to actual sloped area (e.g., 4/12 pitch = 1.054)
- roofing_squares: Total roof area in "squares" (100 sqft each)
- bundles: Bundles of shingles (3 bundles = 1 square)
- underlayment_rolls: Rolls of 15lb felt or synthetic underlayment (400 sqft/roll)
- drip_edge_ft: Linear feet of metal drip edge for eaves and rakes
Pro Tips
- One roofing square = 100 sq ft of roof surface. Most shingles come 3 bundles per square.
- Always use drip edge along eaves (bottom edges) and rakes (side edges) to prevent water damage
- Install ice-and-water shield in the first 3ft from eaves in cold climates — it prevents ice dam damage
- For valleys, add 15% extra shingles to account for weaving or cutting at valley lines
- Synthetic underlayment (felt substitute) is lighter, faster to install, and more durable than 15lb felt
Recommended Products
Frequently Asked Questions
How many bundles of shingles do I need for a 1,500 sq ft roof?
1,500 sqft of actual roof area = 15 roofing squares × 3 bundles = 45 bundles. Add 10–15% waste = 50–52 bundles. Note: this is actual roof area, not footprint — factor in your pitch multiplier.
How many roofing squares in a bundle of shingles?
Three bundles of standard architectural shingles cover one roofing square (100 sqft). Some premium shingles or heavier 3-tab shingles may come at different coverages — always check the manufacturer's label.
Do I need to remove old shingles before reroofing?
Most building codes allow one layer of shingles over existing shingles without removal. Two or more existing layers usually require tear-off. Always check local codes. Tear-off adds cost but allows inspection of roof deck and better longevity.
What is the difference between 15lb and 30lb felt underlayment?
15lb felt (also called #15) is the traditional lightweight option. 30lb (#30) is heavier and more durable. Modern synthetic underlayments are superior to both — they are lighter, stronger, resist tearing, and have better UV resistance during installation.
How much does a roofing square cost?
Material only: 3-tab shingles run $80–$120/square; architectural shingles $100–$150/square; premium architectural $150–$250/square. Installed cost including labor typically runs $350–$600/square depending on region and complexity.