Roofing Calculator
Measure from the ground. Order for the roof.
Turn your footprint and pitch into roof area, squares and shingle bundles.
Your roofing estimate
Measure on the ground.
Skip the ladder.
Add each roof section’s footprint and pitch to begin.
Roof sections
How much waste to allow?
| Waste | Squares | Bundles |
|---|
Comparisons at 0%, 10% and 15% waste. Complex roofs with valleys and dormers usually need more.
Geometry estimates only. Measure from the ground or from plans where possible; this tool does not assess roof safety, structure or building-code requirements.
How do you calculate roof area?
Measure the horizontal footprint the roof covers, including the eaves, then multiply it by the pitch multiplier: √(1 + (pitch ÷ 12)²). A 6:12 roof has a multiplier of 1.118, so every 1,000 ft² of footprint carries about 1,118 ft² of roof surface.
For a simple gable or hip roof with one pitch on every plane, the same multiplier applies to the whole footprint, so both shapes have the same surface area. Sections with different pitches, such as a garage, are calculated separately and added.
The formula, made visible.
Roof area = footprint area × √(1 + (rise ÷ run)²).
Squares = roof area in ft² ÷ 100. Squares to order = squares × (1 + waste ÷ 100). Bundles = squares to order × bundles per square, rounded up once.
A 40 × 30 ft house at 6:12 and a 20 × 20 ft garage at 4:12 have 1,341.641 ft² and 421.637 ft² of roof: 1,763.278 ft², or 17.633 squares. With 10% waste that is 19.396 squares and 59 bundles at 3 per square; with no waste, 53 bundles.
Metric: a 12 × 9 m footprint at 30° has 124.708 m² of roof (13.423 squares). With 10% waste, 45 bundles at 3 per square.
Roof pitch multiplier chart
Multiply the footprint by these factors to get the sloped roof area. Values are exact geometry, rounded to three decimals.
| Pitch | Angle | Multiplier | Roof area per 1,000 ft² footprint |
|---|---|---|---|
| 1:12 | 4.76° | 1.003 | 1,003 ft² |
| 2:12 | 9.46° | 1.014 | 1,014 ft² |
| 3:12 | 14.04° | 1.031 | 1,031 ft² |
| 4:12 | 18.43° | 1.054 | 1,054 ft² |
| 5:12 | 22.62° | 1.083 | 1,083 ft² |
| 6:12 | 26.57° | 1.118 | 1,118 ft² |
| 7:12 | 30.26° | 1.158 | 1,158 ft² |
| 8:12 | 33.69° | 1.202 | 1,202 ft² |
| 9:12 | 36.87° | 1.250 | 1,250 ft² |
| 10:12 | 39.81° | 1.302 | 1,302 ft² |
| 11:12 | 42.51° | 1.357 | 1,357 ft² |
| 12:12 | 45.00° | 1.414 | 1,414 ft² |
How many squares is a 2,000 sq ft roof footprint?
With a 2,000 ft² footprint including eaves, a 4:12 roof is about 2,108 ft² (21.08 squares), 6:12 is 2,236 ft² (22.36 squares) and 8:12 is 2,404 ft² (24.04 squares). With 10% waste at 3 bundles per square, that is 70, 74 and 80 bundles. A two-story home’s living area is not its roof footprint, so measure the footprint itself.
Adding the eaves
A 40 × 30 ft footprint with a 12 in overhang on every side becomes 42 × 32 ft, or 1,344 ft². At 6:12 that is 1,502.638 ft² of roof and, with 10% waste, 50 bundles.
Before you order.
What is a roofing square?
A square is 100 square feet of roof surface. Shingles, underlayment and labor are often priced per square. Divide the roof area in square feet by 100 to get squares.
How many bundles of shingles are in a square?
Standard 3-tab and architectural asphalt shingles are usually packaged at 3 bundles per square, about 33.3 ft² per bundle. GAF notes that some specialty shingles need 4 or 5 bundles per square, so check the coverage printed on your product.
How much waste should I add for shingles?
GAF recommends adding 10–15% for trim and waste. Roofs with many valleys, hips or dormers can need more. The calculator starts at 10% and shows 0%, 10% and 15% side by side.
Do hip roofs have more area than gable roofs?
Not if every plane has the same pitch and the footprint and eaves are the same: the surface area is footprint × the same pitch multiplier. Hip roofs usually need more cutting, so allow more waste and more hip and ridge cap shingles.
How do I find my roof pitch without climbing up?
Use plans, a pitch measured from inside the attic, or a gable-end photo with a known reference. Then convert rise and run, or an angle, with the Roof Pitch Calculator.
What is not included?
Ridge cap, starter strip, underlayment, drip edge, flashing and valley material are not itemized. Dormer and skylight areas are not subtracted. Ask your supplier for those accessories based on the measured lengths.
Method & privacy
Each section’s footprint (with overhang added to each side for length × width sections) is multiplied by √(1 + r²), where r is rise ÷ run. Unit conversions use exact definitions: 1 ft = 0.3048 m and 1 ft² = 0.09290304 m². Inputs stay in this browser; measurements are not stored or sent to our servers. Results use full precision, with at most three decimals displayed, and bundles round up once for the whole roof. Source for bundles and waste: GAF, “How Many Bundles of Shingles Are in a Square?”