Ordering the right amount of shingles means fewer trips to the supply yard and less wasted material sitting in your driveway. The process is straightforward if you follow each step in order: measure your roof area, adjust for pitch, convert to roofing squares, apply a waste factor, and then convert squares to bundles based on your shingle type.
Step 1: Measure Your Roof Area
Start with the flat footprint of your roof. If you have a simple gable roof, this is the building length multiplied by the building width (eave to ridge, measured horizontally). For complex roofs with multiple sections, measure each rectangular or triangular section separately and add them together.
You can measure from the ground using the building dimensions, from inside the attic, or from aerial/satellite imagery. The roof area calculator can help you work through this if you have basic dimensions.
Step 2: Apply the Pitch Factor
A flat measurement underestimates the actual roof surface because the slope adds area. Multiply your footprint area by the pitch factor for your roof slope:
| Pitch | Pitch Factor | Area Increase |
|---|---|---|
| 4:12 | 1.054 | +5.4% |
| 6:12 | 1.118 | +11.8% |
| 8:12 | 1.202 | +20.2% |
| 10:12 | 1.302 | +30.2% |
| 12:12 | 1.414 | +41.4% |
If you do not know your roof pitch, you can measure it with a level and tape measure from the attic or use a smartphone inclinometer app from the ground.
Step 3: Convert to Roofing Squares
The roofing industry measures materials in “squares.” One roofing square equals 100 square feet of roof surface. Divide your adjusted roof area by 100:
Squares = Adjusted Roof Area / 100
For example, if your adjusted area is 1,803 square feet: 1,803 / 100 = 18.03 squares.
Step 4: Add a Waste Factor
You will always use more material than the net roof area due to cuts, overlaps at valleys and hips, starter courses, and damaged shingles. The appropriate waste percentage depends on your roof complexity:
| Roof Type | Waste Factor | Description |
|---|---|---|
| Simple gable | 10% | Two flat planes, minimal cuts |
| Hip roof or moderate complexity | 15% | Hip edges, a few valleys, dormers |
| Complex / cut-up roof | 20% | Multiple valleys, dormers, turrets, steep pitch |
Multiply your squares by (1 + waste factor). Using the earlier example with a hip roof: 18.03 × 1.15 = 20.73 squares.
Step 5: Convert Squares to Bundles
The number of bundles per square depends on the shingle type:
| Shingle Type | Bundles per Square | Notes |
|---|---|---|
| 3-tab shingles | 3 | Standard; consistent across manufacturers |
| Architectural (dimensional) | 3 to 5 | Heavier; check manufacturer specs |
| Premium / designer | 4 to 5 | Thicker profiles; varies by product line |
For standard 3-tab shingles: 20.73 squares × 3 bundles = 62.2, so you would order 63 bundles. For architectural shingles at 4 bundles per square: 20.73 × 4 = 82.9, so you would order 83 bundles. Always round up — you cannot buy partial bundles.
Starter Strip and Ridge Cap Estimation
Starter strips run along the eaves and rakes (the bottom and side edges of the roof). Measure the total linear feet of eave and rake edges. Starter strip shingles are typically sold in bundles covering approximately 100 to 120 linear feet per bundle, though this varies by manufacturer.
Ridge cap shingles cover the peak(s) where two roof planes meet. Measure the total linear feet of ridges and hips. Ridge cap bundles commonly cover approximately 20 to 35 linear feet per bundle depending on the product. Check the specific coverage listed on the packaging for accurate ordering.
Worked Example
Suppose you have a hip roof with a footprint of 30 feet by 50 feet and a 6:12 pitch:
- Footprint area: 30 × 50 = 1,500 sq ft
- Apply pitch factor: 1,500 × 1.118 = 1,677 sq ft
- Convert to squares: 1,677 / 100 = 16.77 squares
- Add 15% waste (hip roof): 16.77 × 1.15 = 19.29 squares
- Convert to bundles (3-tab): 19.29 × 3 = 57.9 → order 58 bundles
- Convert to bundles (architectural at 4/sq): 19.29 × 4 = 77.2 → order 78 bundles
Use the shingle calculator to run these numbers automatically with your own measurements.
Common Mistakes
- Forgetting the pitch factor. Using the flat footprint area without adjusting for slope underestimates material by up to 41% on steep roofs.
- Using the wrong bundles-per-square number. Architectural shingles are heavier and may require 4 or 5 bundles per square. Always check the manufacturer’s packaging or spec sheet.
- Skipping waste entirely. Even a simple gable needs 10% waste for starter courses, cuts at rakes, and any shingles damaged during installation.
- Forgetting ridge caps and starter strips. These are separate products from field shingles and must be ordered in addition to your bundle count.
- Ordering exactly the calculated amount. Round up, not down. Having 2-3 extra bundles is better than stopping mid-job for a supply run. Unopened bundles can usually be returned.
Sources and Notes
The 3-bundles-per-square standard for 3-tab shingles is an industry-wide convention based on standard shingle dimensions (approximately 36 inches by 12 inches with a 5-inch exposure). Architectural shingle bundle counts vary by manufacturer and product weight — always verify with the specific product datasheet. Waste factor recommendations (10%/15%/20%) are general guidelines used across the roofing trade and may need adjustment for unusual roof geometries.