How many bundles of shingles
Bundles are roof area, plus cutting waste, divided by what one bundle covers. Nothing else. The part people get wrong is which coverage to use and when to round.
Three bundles to the square is a rule of thumb, not an arithmetic. It holds for a GAF Timberline HDZ bundle, which covers 33.33 square feet — three of those are 100 exactly. It does not hold for an Owens Corning Oakridge bundle at 32.8 square feet: three cover 98.4, and over 30 squares that shortfall is two bundles.
| Roof | Squares | Bundles at 10% |
|---|---|---|
| 1,000 ft² | 10.00 | 34 |
| 1,341.6 ft² (40 × 30 at 6:12) | 13.42 | 45 |
| 1,500 ft² | 15.00 | 50 |
| 2,000 ft² | 20.00 | 67 |
| 3,000 ft² | 30.00 | 100 |
Those are HDZ bundles at 33.33 square feet with 10 per cent waste. Pick a different bundle in the table of ways to buy and the count moves with its coverage. The three are three shingles, not three sizes of one, so the table never mixes them: you buy one roof's worth of one product.
Round last, not first
A roof of 1,265 square feet is 12.65 squares. Rounding that to 13 and then multiplying by three bundles gives 39. Multiplying first — 1,265 × 1.10 ÷ 33.33 — gives 41.7, so 42 bundles. Three bundles is about $126 and a second trip to the yard. This page never rounds the squares before it divides, and the "how this was worked out" block shows the unrounded figure so you can see it.
Starter and cap are not bundles of shingles
The starter course and the ridge cap come in bundles too, and they are not field shingles: a bundle of GAF Pro-Start runs 120 linear feet, a bundle of Seal-A-Ridge runs 25. They are counted by edge length, not by area, and they are on the shopping list below with their own rows.
Cutting three tabs off field shingles to make your own starter works and saves the starter bundles, but it eats field shingles and voids some wind warranties. If you plan to do it, add the field bundles the starter would have been and leave the starter row unticked.