How many bundles of shingles do I need?
Three bundles to a square, and a square is 100 square feet of roof — not of floor. Bundle counts by footprint, with the pitch already allowed for.
A 28' × 40' house at 6/12 takes 47 bundles — 15.5 squares.
That is 1409 ft² of actual roof, which is well over the footprint because the roof is sloped and overhangs the walls on every side.
How that is worked out
- Start from the plan area including the overhang, not the floor area: 1260 ft².
- Multiply by the slope factor for the pitch — 1.1180 at 6/12 — to get the real sloped area: 1409 ft².
- Add 10% for waste, divide by 100 ft² per square, and multiply by 3 bundles per square: 47 bundles.
Simple gable roof at 6/12, 12" overhang, 10% waste
| Footprint | Roof area | Squares | Bundles | Underlayment rolls | Nails |
|---|---|---|---|---|---|
| 20' × 30' | 787 ft² | 8.7 | 26 | 1 | 8320 |
| 24' × 36' | 1105 ft² | 12.2 | 37 | 2 | 11840 |
| 28' × 40' | 1409 ft² | 15.5 | 47 | 2 | 15040 |
| 30' × 50' | 1860 ft² | 20.5 | 62 | 3 | 19840 |
| 36' × 60' | 2634 ft² | 29.0 | 87 | 3 | 27840 |
| 40' × 60' | 2911 ft² | 32.0 | 97 | 4 | 31040 |
Worth knowing
- A square is 100 ft² of roof and takes 3 bundles of standard three-tab or architectural shingles. That ratio holds across every maker, which is why roofers talk in squares rather than bundles.
- 10% waste suits a plain gable. Hips, valleys and dormers all cut into full shingles, so a complicated roof wants 15% or more — and a roof with several valleys can want 20%.
- Starter course and ridge cap are separate products and are not in these figures. Both are bought by the linear foot of eave and ridge.
- Tearing off the old roof first? Check the deck before ordering. Soft or delaminated sheathing is found on the day and adds sheets of plywood to the order.
Work out your own numbers
- Roofing calculator
Squares, bundles, starter strip, ridge cap and underlayment from a building footprint and a pitch.
- Rafters
Common, hip and jack rafters for any pitch, with the birdsmouth laid out and the cut angles alongside.
Related questions
- How many bundles of shingles in a square?
- Three, for standard three-tab and most architectural shingles. A square covers 100 square feet of roof. Some heavyweight and designer shingles run four or five bundles to the square, so check the wrapper — but three is what to plan around.
- How do I calculate roof area from the floor plan?
- Take the plan area including the overhangs, then multiply by the slope factor for your pitch — 1.118 at 6/12, 1.202 at 8/12. That factor is hypot(12, rise) ÷ 12, and it converts a flat footprint into the sloped surface over it. Skipping it undercounts a 6/12 roof by more than a tenth.
- How much extra should I order for waste?
- 10% on a simple gable, 15% on anything with hips and valleys, and more again if the roof is cut up with dormers. Valleys are the expensive part — every course gets cut on an angle and the offcut is usually too small to use.