Roof Square Footage: How to Calculate
Quick answer: multiply your home's footprint by a pitch factor. A 1,200 sq ft floor plan with a 6/12 roof is about 1,344 sq ft of roof surface — that number is what you order shingles by.
- Footprint × pitch
- What a square is
- Pitch factor chart
- Worked example
- Common mistakes
Footprint × pitch
Start with the footprint — the area of the house seen from above (length × width). Then multiply by a pitch factor that accounts for the slope. The factor is 1.0 for a flat roof and climbs to ~1.4 for a steep 12/12. This gives you the true roof surface area.
What a square is
Roofers measure in squares: one square = 100 sq ft of roof surface. Shingles come in bundles, and 3 bundles cover 1 square. So divide your roof area by 100 to get squares, then multiply by 3 for bundle count — the roof calculator does this conversion automatically.
Pitch factor chart
| Roof pitch | Pitch factor | Example (1,200 sq ft) |
|---|---|---|
| Flat – 2/12 | 1.00–1.02 | ~1,200–1,224 |
| 4/12 | 1.05 | ~1,260 |
| 6/12 | 1.12 | ~1,344 |
| 9/12 | 1.25 | ~1,500 |
| 12/12 | 1.41 | ~1,692 |
Pitch factor is why two same-footprint homes can need very different shingle amounts.
Worked example
A 1,600 sq ft footprint (40 × 40) at a 6/12 pitch:
- Add overhangs (~1 ft each side) → ~42 × 42 ≈ 1,764 sq ft
- Pitch factor 1.12 → roof surface ≈ 1,976 sq ft
- Squares: 1,976 ÷ 100 ≈ 20 squares → ~60 bundles
The roof calculator applies the factor and adds waste for you.
Common mistakes
- Ordering by footprint, not roof area. Under-buys shingles.
- Ignoring overhangs. Eaves add real surface.
- Guessing the pitch factor. It changes the count a lot.
- No waste allowance. Valleys and cuts need ~10% extra.
FAQ
Multiply the home's footprint (floor-plan area) by a pitch factor. For a 6/12 roof the factor is about 1.12, so a 1,200 sq ft footprint is roughly 1,344 sq ft of roof surface.
In roofing, a square is 100 square feet of roof surface. Shingles are sold in bundles that cover 3 bundles per square, so you order by the number of squares.
Steeper pitches add significant surface. A 12/12 roof is about 40% more surface than flat, while a standard 6/12 adds about 12%. The pitch factor multiplies your floor-plan area to find true roof area.
Yes — for shingle ordering you measure the full roof surface including overhangs and eaves. Add roughly 1 foot beyond the exterior wall on each side to the footprint before applying the pitch factor.