Roofing Calculator
To estimate roofing, multiply your home's footprint (length × width) by a pitch factor, then divide by 100 to get squares. Add 10–15% for waste. Shingles come 3 bundles per square. A 40×30 ft home with a 6:12 roof needs about 14.8 squares and costs roughly $5,900–$10,300 installed.
- 1 roofing square
- 100 ft²
- Bundles per square
- 3
- Typical waste
- 10–15%
Your measurements
Pitch is the rise in inches per 12 inches of run.
Enter your measurements
Fill in the fields to see your estimate.
The formula
Squares = Footprint × pitch factor × (1 + waste %) ÷ 100; Bundles = squares × 3How to calculate it manually
- 1
Measure the footprint
Use the building's length × width at ground level.
- 2
Apply the pitch factor
A steeper roof has more surface — e.g. 6:12 multiplies area by 1.118.
- 3
Convert to squares
Divide total roof area by 100. One square = 100 sq ft.
- 4
Add waste and bundles
Add 10–15%, then multiply squares by 3 for shingle bundles.
Example calculation
A 40 ft × 30 ft home = 1,200 ft² footprint × 1.118 (6:12) × 1.10 waste ≈ 1,476 ft² = 14.8 squares ≈ 45 bundles.
Roofing material cost & lifespan
Installed cost per square (100 ft²), including materials and labor. Prices vary by region.
| Material | Cost per square (installed) | Lifespan | Best for |
|---|---|---|---|
| 3-tab asphalt shingles | $350 – $500 | 15–20 yrs | Budget re-roofs |
| Architectural shingles | $450 – $700 | 25–30 yrs | Most homes |
| Metal roofing | $800 – $1,400 | 40–70 yrs | Longevity, snow |
| Wood shake | $600 – $1,000 | 25–30 yrs | Premium look |
| Slate / tile | $1,000 – $2,000 | 50–100 yrs | High-end, fire zones |
Roof pitch reference
Pitch is the vertical rise in inches per 12 inches of horizontal run.
| Pitch | Area multiplier | Description |
|---|---|---|
| 0–2:12 | 1.02 | Flat / low slope |
| 4:12 | 1.054 | Walkable, gentle |
| 6:12 | 1.118 | Most common |
| 8:12 | 1.202 | Steep, hard to walk |
| 12:12 | 1.414 | Very steep (45°) |
Common roofing estimating mistakes
Ignoring roof pitch
Using the footprint alone underestimates a sloped roof's true surface area. Always apply a pitch multiplier.
Skipping the waste factor
Hips, valleys, and starter/ridge courses create offcuts. Add 10% for simple roofs and 15% for cut-up roofs.
Forgetting accessories
Underlayment, drip edge, ridge cap, and flashing aren't counted in shingle bundles — budget for them separately.
Measuring from the ground
Eaves and overhangs extend past the walls. Measure the actual roof plane, not the building's footprint, when you can.
Frequently asked questions
Related guides
Related calculators
Ready to start your roofing project?
Run the numbers above, then explore related tools and guides to plan every step.