Bags of concrete per cubic yard
A cubic yard is 27 cubic feet. Divide that by what one bag yields and you get the bags per yard — 45 for the standard 80 lb bag. The smaller the bag, the more of them it takes. These are the same yields the slab calculator uses.
| Bag size | Yield (ft³) | Bags / yd³ | Bags / ½ yd³ |
|---|---|---|---|
| 40 lb | 0.300 | 90 | 45 |
| 50 lb | 0.375 | 72 | 36 |
| 60 lb | 0.450 | 60 | 30 |
| 80 lb | 0.600 | 45 | 23 |
| 90 lb | 0.675 | 40 | 20 |
Why it takes so many bags
The count surprises people, and the reason is just the size of a cubic yard:
- A yard is 27 ft³: a 3 ft cube — far more volume than it looks stacked on a pallet.
- A bag yields a fraction of that: an 80 lb bag makes 0.60 ft³ of set concrete, so it takes 45 to fill the yard.
- Weight adds up: 45 × 80 lb is 3,600 lb of mix — near two tons to haul, open and blend by hand.
- Water isn’t extra volume: the yield is the finished, mixed concrete — the water is already counted.
- Switch to ready-mix past ~½ yard: the bag premium and the labor both cross over around there.
What one 80 lb bag covers
For slabs and pads, coverage per bag falls as the slab gets thicker — an 80 lb bag (0.60 ft³) spreads over less area the deeper you pour:
| Thickness | Covers | Bags / 100 ft² |
|---|---|---|
| 2 in | 3.6 ft² | 28 |
| 3 in | 2.4 ft² | 42 |
| 4 in | 1.8 ft² | 56 |
| 6 in | 1.2 ft² | 84 |
Concrete bag FAQ
How many 80 lb bags of concrete make a cubic yard?
It takes 45 bags of 80 lb concrete mix to make one cubic yard. An 80 lb bag yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags. That is a lot of mixing — most people order ready-mix once they pass about a half a yard.
How many 60 lb bags of concrete are in a yard?
Sixty bags. A 60 lb bag yields about 0.45 cubic feet, so 27 ÷ 0.45 = 60 bags per cubic yard. Stepping down a bag size means noticeably more bags: the 60 lb bag takes 60 to the yard where the 80 lb takes 45.
How many 40 lb bags of concrete are in a yard?
Ninety bags. A 40 lb bag yields about 0.30 cubic feet, so 27 ÷ 0.30 = 90 bags to the cubic yard — double the count of 80 lb bags for the same volume. Small bags are easier to carry but you handle twice as many.
How many bags of concrete do I need for a 10x10 slab?
A 10 × 10 ft slab at 4 in thick is about 1.23 cubic yards, which is roughly 56 bags of 80 lb before waste. At that size the bags add up fast — 56 bags is well over a ton of mix to haul and blend — so a short-load of ready-mix is usually the better call.
Is it cheaper to mix bags or order ready-mix?
For small jobs — footings, a few post holes, a small pad — bagged mix is cheaper and there is no delivery minimum. Past roughly half a cubic yard, ready-mix usually wins on both cost and labor, because 45 bags a yard is a lot of lifting, and short-load fees are less than the bag premium at volume.
How much does a bag of concrete yield?
By bag weight: 40 lb yields about 0.30 ft³, 50 lb about 0.375, 60 lb about 0.45, 80 lb about 0.60, and 90 lb about 0.675 ft³. These are the published mixed yields — the actual set concrete a bag makes once water is added, which is what the bags-per-yard math is built on.
How much area does an 80 lb bag of concrete cover?
About 1.8 ft² at 4 in thick, since 0.60 ft³ ÷ (4 ÷ 12 ft) = 1.8 ft². The same bag covers 2.4 ft² at 3 in and 1.2 ft² at 6 in — coverage falls as the slab gets thicker. To cover 100 ft² at 4 in you need 56 bags of 80 lb.
Sources and standards
The yields are the manufacturers’; the arithmetic is fixed:
- Published bag yields: the mixed set-concrete yield per bag (40 lb ≈ 0.30 ft³ … 80 lb ≈ 0.60 ft³) from Quikrete/Sakrete data.
- 27 ft³ per cubic yard: exact — a cubic yard is 3 × 3 × 3 ft.
- Bags per yard: 27 ÷ bag yield, rounded up to whole bags — the numbers in Table 1.
- Ready-mix crossover: a rule of thumb, not a spec — local bag prices and short-load fees set the real break-even.