Roofing Calculator
Calculate roof area, roofing squares and shingle bundles for any footprint and pitch — from 3/12 to 12/12.
A 20×30 ft roof footprint at 6/12 pitch covers 671 sq ft — about 7 roofing squares and 21 bundles of shingles (8 squares and 24 bundles with 10% waste).
How to Use This Roofing Calculator
- Enter the footprint of the roof — the area it covers at ground level — in feet.
- Enter the roof pitch as rise over run (e.g. 6/12 = 6 in of rise per 12 in of run).
- Read the roof area, roofing squares and shingle bundles (3 bundles per square).
- Add the waste percentage — 10% is typical for shingle roofs.
The Formula
Roof area = footprint × pitch factor. The pitch factor comes from the Pythagorean theorem: factor = √(1 + (rise/run)²). A roofing square is 100 sq ft — the industry unit for ordering. Standard asphalt shingles come 3 bundles per square.
Factor = √(1 + (rise/run)²)6/12 → 1.118 · 8/12 → 1.202 · 12/12 → 1.414Area = footprint × factorRoof surface in sq ftSquares = area ÷ 1001 roofing square = 100 sq ftBundles = squares × 3Standard asphalt shinglesWorked Example: 20×30 Roof at 6/12
A 20×30 ft footprint is 600 sq ft. At 6/12 pitch (factor 1.118): 600 × 1.118 = 671 sq ft of roof = 6.71 squares → 7 squares. At 3 bundles per square: 21 bundles (24 with 10% waste).
Pitch Factors and Squares
| Pitch (rise/run) | Roof factor | Squares per 1,200 ft² footprint |
|---|---|---|
| 3/12 | 1.031 | 13 |
| 4/12 | 1.054 | 13 |
| 6/12 | 1.118 | 14 |
| 8/12 | 1.202 | 15 |
| 12/12 | 1.414 | 17 |
Squares rounded up. Example: 1,200 × factor ÷ 100.
How to Measure Roof Pitch
Pitch is the rise in inches for every 12 in of horizontal run. Measure 12 in out from the roof edge with a level, then read the vertical drop — that is your rise. A 6 in drop is 6/12. Steeper roofs shed snow and water faster but are harder and more dangerous to work on — and they need more material because the surface area grows with the pitch.
Quick Tips
- A roofing square is 100 sq ft — suppliers quote in squares, not sq ft.
- Order 10% extra for starter strips, ridge caps and waste.
- Include valleys and eaves in the footprint for a closer estimate.
Frequently Asked Questions
What is a roofing square?
A roofing square is 100 square feet of roof surface — the standard unit used by roofing suppliers.
How many bundles of shingles are in a square?
3 bundles of standard asphalt shingles cover one roofing square (100 sq ft).
How do I measure roof pitch?
Hold a level 12 in out from the roof, then measure the vertical drop. A 6 in drop over 12 in of run is a 6/12 pitch.
How many squares do I need for a 2,000 sq ft house?
Depends on the pitch: a 2,000 sq ft footprint at 6/12 is about 2,236 sq ft of roof = 23 squares (25 with waste).