Roofing Calculator
Multiply the footprint by the pitch multiplier, add waste, and divide by 100 for squares: a 40 × 30 ft footprint at 6/12 is 1,342 sq ft of roof, 14.8 squares with 10% waste, or 45 bundles at 3 per square.
Roofing estimate
How to estimate shingles
roof area = footprint length × width × pitch multiplier squares = roof area × (1 + waste %) ÷ 100 bundles = squares × bundles per square, rounded up
Worked example: a 40 × 30 ft footprint (overhangs included) is 1,200 sq ft. At 6/12 the multiplier is 1.118, so the roof is 1,342 sq ft. Add 10%: 1,476 sq ft, or 14.76 squares. At 3 bundles per square that is 44.27, rounded up to 45 bundles.
Measuring on the roof instead? Multiply each plane's length by its slope length (eave to ridge) and add them up; the pitch is already built in, so skip the multiplier.
Bundles per square by product
| Product | Bundles per square | Coverage per square |
|---|---|---|
| GAF Timberline HDZ | 3 | 98.4 sq ft |
| Owens Corning TruDefinition Duration | 3 | 98.4 sq ft |
| Owens Corning Supreme (3-tab) | 3 | 100 sq ft |
| Heavier laminated shingles (Fine Homebuilding) | 4 or 5 | check wrapper |
Starter strip and ridge cap
Starter shingles run along every eave and rake; ridge caps run along ridges and hips. The calculator assumes a simple gable when you leave these blank: both long eaves plus four rake edges, and one ridge the length of the footprint. Measure hips and extra ridges on anything more complex.
- GAF Pro-Start starter: about 120.33 lineal ft per bundle.
- GAF Seal-A-Ridge: 4 bundles cover about 100 lineal ft (25 ft per bundle).
- 3-tab shingles cut into caps: about 35 ft of ridge per bundle (Fine Homebuilding).
How much extra to buy
The calculator defaults to the 10% allowance from IKO's worked example. A plain gable with few cuts wastes less: Mike Guertin figures about 1%. Complex roofs with open valleys, dormers and hips need 5% or more. Slopes under 2/12 cannot take asphalt shingles at all (IRC R905.2.2).
Frequently asked questions
How many bundles of shingles are in a square?
Three for most shingles. GAF Timberline HDZ, Owens Corning TruDefinition Duration and Owens Corning Supreme 3-tab all list 3 bundles per square. Fine Homebuilding notes that heavier laminated shingles can take 4 or sometimes 5 bundles, so check the wrapper.
What is a roofing square?
A square is the amount of shingles needed to cover 100 sq ft of roof. GAF and Owens Corning laminated shingles list 98.4 sq ft of coverage for their 3-bundle square.
How many squares is a 2,000 sq ft roof?
2,000 ÷ 100 = 20 squares before waste. With a 10% allowance that is 22 squares, or 66 bundles at 3 bundles per square. Note that a 2,000 sq ft house usually has more than 2,000 sq ft of roof once overhangs and pitch are counted.
How much waste should I add for shingles?
IKO's estimating guide uses a 10% waste allowance in its worked example. Fine Homebuilding's Mike Guertin uses about 1% on a simple roof and 5% or more on a complex roof with open valleys. Hips, valleys and dormers mean more cutting, so more waste.
How much starter strip and ridge cap do I need?
Measure the eaves and rakes for starter and the ridges and hips for ridge cap, then divide by the coverage on the bundle. GAF Pro-Start covers about 120.33 lineal ft per bundle and GAF Seal-A-Ridge about 25 ft per bundle (4 bundles for 100 ft). Fine Homebuilding says a bundle of 3-tab shingles cut into caps covers about 35 ft of ridge.
Sources
- Don't Fall Short on Shingles: How to Estimate Materials for Roofing Projects (Mike Guertin), Fine Homebuilding. Used for: a square = 100 sq ft; 4 or 5 bundles for heavier shingles; 1% to 5%+ waste; 35 ft of ridge per 3-tab bundle.
- Installation Instructions: Timberline HDZ, UHDZ and related shingles (©2023), GAF (manufacturer PDF, hosted by Home Depot). Used for: 3 bundles cover 98.4 sq ft; 5 5/8 in exposure; minimum slope.
- TruDefinition Duration Shingles product sheet, Owens Corning (manufacturer PDF, hosted by Home Depot). Used for: 3 bundles per square, 98.4 sq ft.
- Supreme (3-tab) Shingles product sheet, Owens Corning (manufacturer PDF, hosted by Lowe's). Used for: 3-tab: 3 bundles per square, 100 sq ft.
- Pro-Start Starter Strip Shingles product sheet, GAF (manufacturer PDF, hosted by Home Depot). Used for: starter strip coverage 120.33 lineal ft per bundle.
- Seal-A-Ridge Ridge Cap Shingles sell sheet (©2023), GAF (manufacturer PDF, hosted by Taiga Building Products). Used for: ridge cap coverage, 4 bundles per 100 lineal ft.
- Estimating How Much Roofing Is Required, IKO. Used for: 10% waste allowance example; area factors by pitch.
- Asphalt Shingles (IRC R905.2), City of Hopkins, MN. Used for: IRC R905.2 minimum slope 2:12.
Estimates only. Check local codes and your product's label. Found a number that does not match its source? Send a correction.