How Much Do I Need?

Roofing Shingle Calculator

How many bundles of shingles do I need?

Enter the length and width of the roof as seen from above, including the overhangs, and the roof pitch. The calculator turns that flat footprint into the real sloped area, then into squares and bundles.

Units
Roof

Inches of rise per 12 inches of run (e.g. 6 for a 6/12 roof), or degrees.

Shingles

Most asphalt shingles are 3 bundles per 100 ft². Check the wrapper.

About 10% for simple gable roofs, 15% or more for hips, valleys and dormers.

Cost (optional)

Add the price to see an estimated total.

Results update as you type.

Your estimate

Shingles to buy

45 bundles

15 squares for a 1,342 ft² roof, including 10% waste.

Estimated amount to buy

Bundles of shingles
45
Squares (100 ft² each)
15

Calculated quantity (no waste)

Footprint
1,200 ft²
Slope factor for 6/12
1.118
Roof area
1,342 ft² (124.6 m²)
Squares
13.42
How this was calculated
  1. Footprint = 40 ft × 30 ft = 1,200 ft²
  2. Slope factor = √(1 + (6 ÷ 12)²) = 1.118
  3. Roof area = 1,200 ft² × 1.118 = 1,342 ft²
  4. Squares = 1,342 ft² ÷ 100 = 13.42; with 10% waste × 1.1 = 14.76
  5. Bundles = 14.76 × 3 per square = 44.28, rounded up to 45
  • Starter strips, ridge caps, underlayment, drip edge and flashing are extra. Many roofers buy ridge-cap shingles separately.
  • Roof work is dangerous. Use proper fall protection, or hire a roofer.

How the roofing calculation works

  1. Footprint = length × width of the roof seen from directly above, including the overhangs.
  2. Slope factor = √(1 + (rise ÷ 12)²) for a pitch given as rise in 12, or 1 ÷ cos(angle) for degrees. A 6/12 roof has a factor of 1.118, so it has about 12% more surface than its footprint.
  3. Roof area = footprint × slope factor. This works for any roof where every face has the same pitch, including simple gable and hip roofs.
  4. Squares = roof area in square feet ÷ 100, plus the waste allowance.
  5. Bundles = squares × bundles per square, rounded up.

Finding your roof pitch

Pitch is how many inches the roof rises for every 12 inches it runs horizontally. You can measure it from the attic with a level and tape, or from the ground with a phone app. Common pitches: 4/12 (18.4°), 6/12 (26.6°), 8/12 (33.7°) and 12/12 (45°). If parts of your roof have different pitches, calculate each part separately.

Rounding rules

  • Bundles are rounded up after the waste allowance is added.
  • "Squares to buy" is the rounded bundle count ÷ bundles per square.