Roofing Calculator

One roofing square = 100 square feet of roof surface area. It is the standard unit used by roofing contractors and material suppliers for estimating and pricing. Most shingle bundles cover 1/3 of a square (about 33 sq ft), so a typical job is measured in squares and then converted to bundle counts.

A steeper pitch has more actual roof surface than its footprint suggests. A pitch multiplier converts the flat "plan area" to actual sloped area. Multipliers: 4:12 pitch = 1.054×, 6:12 = 1.118×, 8:12 = 1.202×, 12:12 = 1.414×. A 2,000 sq ft footprint with a 6:12 pitch has 2,236 sq ft of actual roof area.

Add 10% waste for standard gable or shed roofs. Add 15% for complex roofs with multiple valleys, hips, or dormers. Ordering a little extra is worthwhile — shingle colours can vary between batches, making repairs with mismatched shingles look bad. Store extras in a dry place for future repairs.

Standard 15-lb felt: 4 square roll (400 sq ft). Standard 30-lb felt: 2 square roll (200 sq ft). Synthetic underlayment: 10 square roll (1,000 sq ft). Divide your total roof area (with waste factor) by roll coverage. Most residential roofs use 30-lb felt or synthetic underlayment for better tear resistance.