Roofing Calculator
Calculate roof area, squares and shingle bundles from footprint and pitch.
About Roofing Calculator
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)
Worked example
With the default values below, Roofing Calculator returns Actual Roof Area (with waste) of 1,475.8. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Roof Footprint Lengthminimum 1 ft
- 40 ft
- Roof Footprint Widthminimum 1 ft
- 30 ft
- Roof Pitch (rise-in-12)one of 2/12 (flat, 9.5°), 3/12 (14°), 4/12 (18.4°), 5/12 (22.6°), 6/12 (26.6°), 7/12 (30.3°), 8/12 (33.7°), 9/12 (36.9°), 10/12 (39.8°), 12/12 (45°)
- 6/12 (26.6°)
- Bundles per Squareone of 3 bundles (3-tab strip shingles), 4 bundles (architectural / dimensional)
- 3 bundles (3-tab strip shingles)
- Waste Factoraccepts 0–30 %
- 10 %
Results
- Actual Roof Area (with waste)
- 1,475.8 sq ft
- Roofing Squares
- 14.76
- Shingle BundlesRounded up.
- 45
- Pitch Multiplier
- 1.1180
- Pitch Angle
- 26.6 °
- Footprint Area
- 1,200.0 sq ft
Step by step
- 1Footprint area= 1200.0 sq ft
- 2Pitch multiplier= 1.1180
- 3Actual sloped area= 1341.6 sq ft
- 4Add 10% waste= 1475.8 sq ft
- 5Roofing squares= 14.76 squares
- 6Bundles needed= 45 bundles
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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 a roof with a single, uniform pitch it is exact — gable, hip and shed roofs over the same footprint all have the same sloped area, because the multiplier scales the whole footprint at once. The number of planes does not change the total. Roofs that mix pitches, or that have dormers adding area outside the footprint, should be measured plane by plane and the results added.
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.