Roofing Calculator
Estimate how many roofing squares, shingle bundles and underlayment rolls you need – and what a new roof will cost – from your house dimensions and roof pitch.
Formulas shown on this page · Last reviewed October 2026
How to use the roofing calculator
- Measure the length and width of the house footprint (outside walls).
- Pick your roof pitch – the rise in inches for every 12 inches of run.
- Enter the eave overhang and a waste factor.
- Optionally enter your local installed price per square to see the total cost.
The formula
roof area = (length + 2 × overhang) × (width + 2 × overhang) × √(1 + (pitch ÷ 12)²)
squares = roof area ÷ 100 × (1 + waste %)
The pitch multiplier converts the flat footprint into the real sloped surface. A 6/12 roof is about 11.8% larger than its footprint; a 12/12 roof is 41.4% larger.
Roof pitch multipliers
| Pitch | Multiplier | Pitch | Multiplier |
|---|---|---|---|
| 3/12 | 1.031 | 8/12 | 1.202 |
| 4/12 | 1.054 | 9/12 | 1.250 |
| 5/12 | 1.083 | 10/12 | 1.302 |
| 6/12 | 1.118 | 11/12 | 1.357 |
| 7/12 | 1.158 | 12/12 | 1.414 |
What else goes on a roof
Beyond shingles, budget for underlayment (one synthetic roll covers about 10 squares), drip edge along every eave and rake, starter strip, ridge cap shingles, ice-and-water shield in valleys and cold climates, and roofing nails (about 2.5 lb per square). Tear-off of an old layer usually adds $100–$150 per square.
Roof size by house square footage
1,000 sq ft house · 1,200 sq ft house · 1,400 sq ft house · 1,500 sq ft house · 1,600 sq ft house · 1,800 sq ft house · 2,000 sq ft house · 2,200 sq ft house · 2,400 sq ft house · 2,500 sq ft house · 2,800 sq ft house · 3,000 sq ft house · 3,500 sq ft house
Frequently asked questions
How many squares is a 2,000 sq ft house roof?
A 2,000 sq ft single-story house with a 6/12 pitch and 12-inch overhangs (about 50 × 40 ft) has roughly 26–27 roofing squares including 10% waste. Steeper pitches and hip roofs need more.
How many bundles of shingles are in a square?
Standard 3-tab and architectural asphalt shingles come 3 bundles per square (100 sq ft). Some heavy designer shingles need 4 or 5 bundles per square.
How much does a new roof cost per square?
Installed asphalt shingle roofs typically run $350–$550 per square in the US. Metal roofing costs about $800–$1,400 per square, and tile or slate can exceed $1,500.
What waste factor should I use?
Use about 10% for simple gable roofs and 15% or more for hip roofs, dormers and valleys, where more shingles are cut.