Roofers price by the roof surface, not the floor plan. Enter your house size and pitch to get the real roof area, how many squares and bundles to order, and what a replacement costs.
How roof area is calculated
A sloped roof has more surface than the ground it covers. The steeper the pitch, the bigger the difference. The calculator adds the overhang to your house size, then multiplies by a pitch factor.
Pitch factor = √(1 + (rise ÷ 12)²)
Roof area = footprint × pitch factor
Squares = roof area × (1 + waste %) ÷ 100
Worked example: a 50 × 30 ft house, 6/12 pitch
With a 12-inch overhang the footprint is 52 × 32 = 1,664 sq ft. A 6/12 pitch factor is 1.118, so the roof surface is 1,860 sq ft. Adding 10% waste gives 20.5 squares, or 62 bundles of shingles. At $5.50 per sq ft installed plus $1.50 per sq ft to tear off one layer, the job comes to about $13,000.
Pitch factors
| Pitch | Multiply footprint by | Typical on |
|---|---|---|
| 3/12 | 1.031 | Ranch homes, porches |
| 4/12 | 1.054 | Ranch and split-level homes |
| 6/12 | 1.118 | Most US houses |
| 8/12 | 1.202 | Colonials, two-story homes |
| 10/12 | 1.302 | Steep Victorian and Tudor styles |
| 12/12 | 1.414 | A-frames, steep gables |
What a new roof costs in 2026
This Old House’s 2026 survey of 1,000 homeowners found that asphalt shingles are the most popular roofing material, and puts the average replacement for a 2,000 sq ft asphalt roof at about $15,400. Installed prices for asphalt generally run from about $4.50 per sq ft for basic 3-tab shingles to $7.50 or more for premium shingles. Metal typically costs two to three times as much as asphalt.
| Item | Typical 2026 price |
|---|---|
| Asphalt shingles, installed | $4.50–$7.50 per sq ft |
| Standing-seam metal, installed | $8–$18 per sq ft |
| Tear-off of old shingles | $1.00–$2.40 per sq ft per layer |
| Decking replacement (if rotten) | $2–$5 per sq ft |
For a deeper breakdown, read our guide to new roof costs in 2026.
Frequently asked questions
What is a roofing square?
A square is 100 sq ft of roof surface. Shingles, underlayment and most contractor quotes are priced per square.
How many bundles are in a square?
Three bundles for most 3-tab and architectural shingles. Some heavy premium shingles need four or five, so check the wrapper.
How do I find my roof pitch?
Hold a level horizontally against a rafter or the roof edge, measure 12 inches along it, then measure straight up to the roof. That height in inches is the pitch: 6 inches means 6/12.
Can I put new shingles over old ones?
Many codes allow two layers at most, and many manufacturers limit warranties on overlays. A tear-off lets the roofer inspect and repair the decking.
Sources: This Old House, New Roof Cost (updated May 2026); 2026 roofing cost guides from JobNimbus and HomeGnome.
