The Roofing Calculator estimates the roof area, roofing squares and shingle bundles needed from the house base area, roof pitch and eave overhang.
Roof area: 2,441 sq ft (24.4 squares)
| Roof area | 2,440.5 sq ft |
| Roofing squares (100 sq ft) | 24.41 |
| Bundles of shingles (3 per square) | 74 |
| Pitch angle | 26.6° |
| Pitch multiplier | 1.1180 |
Pitch is the rise of a roof per 12 units of horizontal run: a 6/12 roof rises 6 inches for every foot, an angle of about 26.6°. Steeper roofs have more surface area for the same footprint and are harder and costlier to work on.
The base area is expanded by the eave overhang on all sides and multiplied by the pitch factor √(1 + (rise/run)²). A 6/12 roof has a factor of 1.118.
Worked example (defaults): a 2,000 sq ft footprint with 1 ft eaves becomes about 2,183 sq ft flat, or about 2,440 sq ft of roof at 6/12, about 24.4 squares or 74 bundles of shingles.
Roofers measure in squares of 100 sq ft. Standard asphalt shingles come three bundles to a square. Add 10–15% for waste, hips, ridges and valleys, and buy starter strips, ridge caps, underlayment and flashing too.
How long does a roof last? Asphalt shingles 20–30 years, metal 40–70, slate and tile 50+.
Is this exact for complex roofs? No; dormers and valleys need individual measuring.
What does a new roof cost? Often $4–$12 per square foot installed, depending on material and region.