Roofing Calculator
Calculate roof area, squares and shingle bundles from footprint and pitch.
Inputs
Horizontal plan view length of the structure.
Rise in inches per 12 inches of run.
Hip roofs use the same pitch multiplier but both directions have slope.
Each facet is one pitched plane. Simple gable = 2.
Add 10% for simple roofs, 15–20% for complex hips with many valleys.
Actual Roof Area (with waste)
1,475.8sq ft
Roofing Squares
14.76
Shingle Bundles
45
Rounded up.
Pitch Multiplier
1.1180
Pitch Angle
26.6°
Footprint Area
1,200.0sq ft
Step by step
Footprint area
40 ft × 30 ft
= 1200.0 sq ft
Pitch multiplier
√(1 + (6/12)²) = √(1 + 0.5000²)
= 1.1180
Actual sloped area
1200.0 × 1.1180
= 1341.6 sq ft
Add 10% waste
= 1475.8 sq ft
Roofing squares
1475.8 ÷ 100
= 14.76 squares
Bundles needed
⌈14.76 × 3⌉
= 45 bundles
How it works
A pitched roof covers more area than its footprint because the surface follows the slope. The pitch multiplier √(1 + (rise/12)²) converts horizontal footprint area to actual roof area — it's the ratio of the rafter length to its horizontal projection. A roofing square is 100 sq ft, the unit used for ordering shingles. Bundles per square depend on the shingle type: 3 for standard 3-tab, 4 for architectural/dimensional.
Formulas
Pitch multiplier
Pitch multiplier = √(1 + (rise/12)²)
- rise
- Inches of rise per 12 inches of run
Actual roof area
Roof area = footprint area × pitch multiplier × (1 + waste%)
Squares and bundles
Squares = area ÷ 100; Bundles = ceiling(squares × bundles_per_square)
Frequently Asked Questions
What is a roofing square?
A roofing square is 100 square feet of roof surface. It's the standard ordering unit for shingles. A 2,000 sq ft roof = 20 squares.
How many bundles per square for my shingles?
Standard 3-tab strip shingles use 3 bundles per square. Architectural (dimensional or laminated) shingles typically require 4 bundles per square because they're heavier. Check your manufacturer's data sheet.
How accurate is the pitch multiplier method?
For simple gable and hip roofs it is exact. Complex roofs with dormers, valleys or multiple pitches should be measured by facet — use the 'Number of Facets' field to account for multiple planes.
What does the footprint area mean?
It's the plan view (bird's-eye) area of the structure the roof covers, not the roof surface itself. If your house is 40 ft × 30 ft, the footprint is 1,200 sq ft. The actual roof area will be larger depending on the pitch.