The pitch multiplier converts the flat footprint into the real sloped surface area, so you don't have to climb on the roof to measure it.
How to use the roofing calculator
- Measure the length and width of the house, and add the overhang (eaves) on each side.
- Choose the roof pitch, the rise in inches per 12 inches of run. 4/12 to 6/12 is common.
- Pick the layout that matches your roof. Hips and valleys create more cutting waste.
- Enter your price per bundle to estimate the shingle cost.
The formula
Pitch multiplier: √(1 + (pitch ÷ 12)²). For a 6/12 roof this is 1.118.
Roof area: footprint length × width × multiplier.
Squares: roof area × (1 + waste %) ÷ 100. Most shingles come 3 bundles per square.
Shingles needed by footprint (6/12 pitch, simple gable, 10% waste)
| Footprint | Roof area | Squares | Bundles |
|---|---|---|---|
| 40 × 25 ft (1,000 sq ft) | 1,118 sq ft | 12.3 | 37 |
| 50 × 30 ft (1,500 sq ft) | 1,677 sq ft | 18.4 | 56 |
| 50 × 40 ft (2,000 sq ft) | 2,236 sq ft | 24.6 | 74 |
| 62.5 × 40 ft (2,500 sq ft) | 2,795 sq ft | 30.7 | 93 |
| 75 × 40 ft (3,000 sq ft) | 3,354 sq ft | 36.9 | 111 |
Frequently asked questions
What is a roofing square?
A roofing square is 100 square feet of roof surface. Most asphalt shingles are packaged 3 bundles per square.
How do I find my roof pitch?
Measure 12 inches horizontally from a point on the roof (or rafter), then measure how far the roof rises over that distance. A 6 inch rise means a 6/12 pitch. Pitch-finder apps also work from the ground.
How many bundles of shingles do I need for a 2,000 sq ft house?
For a 2,000 sq ft footprint with a 6/12 pitch and a simple gable roof, roughly 25 squares or about 74 bundles. Hip roofs and steeper pitches need more.
Does this include ridge cap and starter shingles?
No. Add ridge cap based on the length of ridges and hips, and starter strip based on the length of the eaves and rakes.
Results are estimates for planning and budgeting. Always confirm measurements and product coverage before you buy, and follow local building codes.