Roofing Calculator – Roof Area, Squares and Shingle Bundles

How to calculate roof area

Roof area = (Length + 2 × overhang) × (Width + 2 × overhang) × √(1 + (pitch ÷ 12)²)

A 40 × 30 ft house with 1 ft overhangs covers 42 × 32 = 1,344 ft² seen from above. At a 6/12 pitch the slope adds 11.8%, so the roof surface is about 1,503 ft². With 10% waste that is 16.5 squares, or 50 bundles of shingles at three bundles per square.

The pitch factor works for both gable and hip roofs, because every slope of a simple roof has the same pitch. Dormers, valleys and porches add area and waste, so measure them separately for complex roofs.

Pitch factors

Pitch	Factor	Pitch	Factor
3/12	1.031	7/12	1.158
4/12	1.054	8/12	1.202
5/12	1.083	9/12	1.250
6/12	1.118	12/12	1.414

Squares, bundles and other materials

Roofers measure in squares of 100 ft². Most three-tab and architectural shingles come three bundles to a square (some heavy designer shingles use four or five). Add about 10% waste for gable roofs and 15% for hip roofs, which have more cuts. You will also need underlayment (synthetic rolls usually cover 10 squares), drip edge for the eaves and rakes, starter strip and ridge cap. Shingles with a standard four-nail pattern take about 320 nails per square; high-wind areas require six nails.

Roofs under 4/12 need extra underlayment, and shingles are generally not allowed below 2/12. Use a professional for steep or high roofs: falls are the leading cause of construction deaths.

Frequently asked questions

How many bundles of shingles do I need?

Divide the roof area by 100 to get squares, add 10–15% waste, then multiply by three bundles per square.

How do I find my roof pitch?

Hold a level 12 in long against the roof and measure how many inches the roof rises over that run. A 6 in rise is a 6/12 pitch.

How big is a roofing square?

A square is 100 square feet of roof surface.

Last reviewed October 2026. Results are estimates; check important decisions with a qualified professional.