Roofing Calculator

Calculate how many shingle bundles, squares, underlayment rolls, and nails you need for a roof. Enter building footprint, pitch, and roof type — get a complete material list with waste.

ft

Length of the building footprint (plan view).

ft

Width of the building footprint (plan view).

Pitch expressed as X:12. Common: 4:12 (walkable), 6:12 (standard), 12:12 (steep).

Hip roofs require more cuts and waste than gable roofs.

How this calculator works

This calculator works in three steps:

  1. Plan area: length × width = building footprint in square feet.
  2. Roof surface area: multiply plan area by the slope multiplier for the chosen pitch. The slope multiplier is √(1 + (rise/12)²) — for example, a 6:12 pitch has a multiplier of 1.118.
  3. Materials: convert sloped area (with waste) into squares (1 square = 100 sq ft), then into bundles (3 bundles per square for standard 3-tab shingles), plus underlayment rolls, nails, and drip edge.

Hip roofs add 5% extra waste because of cuts at the hips and ridges; gable roofs are simpler.

Formula

plan_area = length × width
slope_mult = √(1 + (pitch/12)²)
roof_area = plan_area × slope_mult
roof_area_waste = roof_area × (1 + waste_pct)
  where waste_pct = 0.10 (gable) or 0.15 (hip)
squares = ceil(roof_area_waste / 100)
bundles = squares × 3
rolls_underlayment = ceil(roof_area_waste / 400)
drip_edge = 2 × (length + width)

Example

For a 40 ft × 30 ft gable roof with a 6:12 pitch:

  • plan_area = 40 × 30 = 1,200 sq ft
  • slope_mult(6:12) = √(1 + 0.25) = 1.118
  • roof_area = 1,200 × 1.118 = 1,341.6 sq ft
  • with 10% waste = 1,475.8 sq ft
  • 15 squares = 45 bundles of shingles
  • 4 rolls of underlayment
  • 140 linear ft of drip edge

Important assumptions

  • Standard 3-tab asphalt shingles: 3 bundles per square. Architectural/dimensional shingles may be 3–4 bundles per square — verify with the product spec.
  • Underlayment coverage assumes 400 sq ft per roll (typical for #15 felt or synthetic underlayment).
  • Nail estimate assumes ~1.5 lb of roofing nails per square (coil nails for nail guns).
  • Waste factor: 10% for gable roofs, 15% for hip roofs (extra cuts at hips/valleys).
  • For complex roofs with multiple dormers, valleys, or skylights, add another 5%.
  • This calculator does NOT include ridge vent, flashing, ice & water shield, or starter strip — add those separately.

FAQ

How many bundles of shingles do I need for a 1,200 sq ft roof?
A 1,200 sq ft plan-area roof with a 6:12 pitch has ~1,342 sq ft of sloped roof area. With 10% waste, that's ~1,476 sq ft = 15 squares = 45 bundles of standard 3-tab shingles.
What is a "square" of shingles?
A square is 100 square feet of roof coverage. Standard 3-tab shingles come 3 bundles per square. Architectural shingles may be 3 or 4 bundles per square depending on the product.
How does roof pitch affect the amount of shingles I need?
Steeper pitches have more sloped surface area per square foot of footprint. A 4:12 pitch has a multiplier of 1.054 (5.4% extra), a 6:12 pitch is 1.118 (11.8% extra), and a 12:12 pitch is 1.414 (41.4% extra).
What's the difference between a gable and a hip roof for material calculations?
A gable roof has two slopes and simple cuts. A hip roof has four slopes meeting at hips and ridges, requiring more cuts at the corners. Hip roofs typically need 5% more shingles than gable roofs of the same footprint.
Do I need ice & water shield?
In cold climates, building code requires ice & water shield at the eaves (typically 2 ft inside the exterior wall) and in valleys. In hot climates, it may not be required. Check your local code.