Formula
How the roofing estimate works
- Sloped roof area = plan length × plan width ÷ cos(pitch angle)
- Target coverage = sloped roof area × (1 + waste %)
- Full bundles = target coverage ÷ coverage per bundle, rounded up
Free project planning tool
Roofing calculator
Estimate sloped roof area, waste-adjusted coverage, full shingle bundles, roofing squares, and material cost.
✓ Metric & imperial✓ Transparent assumptions✓ No signup
Shingles & bundlesInstant estimate
Example calculation
A 40 × 24 ft roof footprint at a 22.6° pitch has roughly 1,040 sq ft of sloped area. With 12% waste and 32.3 sq ft per bundle, the estimate rounds up to 37 bundles.
Planning tips
- Use the total horizontal roof footprint, including overhangs.
- Hip roofs, valleys, dormers, and complex cuts generally need more waste.
- Confirm bundle coverage and required underlayment with the product manufacturer.
Common questions
Roofing calculator FAQ
What is a roofing square?
In US roofing, one roofing square equals 100 square feet of roof surface. It is a measurement of area, not a square-shaped bundle.
Does roof pitch increase material quantity?
Yes. A sloped roof has more surface area than its flat plan footprint. The calculator uses the pitch angle to account for that increase.
How much roofing waste should I add?
Simple gable roofs may use about 10%. Roofs with hips, valleys, dormers, or intricate cuts often require a higher allowance.