Roof Calculator — Squares, Bundles & Roof Area
Enter your building size and roof pitch to get the roof surface area, squares, and shingle bundles. No sign-up, no data stored.
Roof materials
How roof material is calculated
The math is simple and exact — no assumptions to adjust for:
- Footprint = (length + 2 × overhang) × (width + 2 × overhang).
- Roof area = footprint × pitch factor.
- Squares = roof area ÷ 100.
- Bundles = squares × bundles per square.
- Cost = squares × price per square (only if you enter a price).
The pitch factor accounts for the extra surface a sloped roof has over its flat footprint — a 12/12 roof is roughly 41% more material than a flat one. Add 5–10% extra for ridges, valleys, starter rows, and waste.
Roof pitch & coverage chart
Pitch factors and how much each covers.
Roof pitch → factor
| Pitch | Pitch factor | Extra vs flat |
|---|---|---|
| 4/12 | 1.054 | +5% |
| 6/12 | 1.118 | +12% |
| 8/12 | 1.202 | +20% |
| 10/12 | 1.302 | +30% |
| 12/12 | 1.414 | +41% |
Shingle bundles per square
| Shingle type | Bundles per square |
|---|---|
| Architectural | 3 |
| Three-tab | 3–4 |
| Luxury / heavy | 4+ |
Last updated: October 2026 · Pitch factors are standard roof geometry. Bundle counts reflect common US asphalt shingle packaging. Get a roofer's measurement for a precise bid — this calculator is an estimate.
Roof calculator FAQ
At 3 bundles per square, a 20-square roof needs about 60 bundles of architectural shingles. Add a few extra for ridges, valleys, and starter rows.
Measure the vertical rise over 12 horizontal inches. If the roof rises 6 inches for every foot of run, it's a 6/12 pitch. You can measure this from the attic with a level and a tape, or from the ground with a pitch gauge.
No — it estimates the field area only. Add extra bundles for hip and ridge cap shingles, valley flashing, and starter courses. A good rule is 5–10% on top of the field count.
Yes. A steeper roof uses more material (higher pitch factor) and is harder and more dangerous to work on, so labor costs rise too. That's why a 12/12 roof costs more per square than a 4/12.
Most codes allow one re-roof over a single existing layer. Tearing off the old layer costs more but reveals the decking and lasts longer. Ask your roofer which your local code allows and what the decking looks like.