One 80 lb bag of concrete mix makes 0.60 cubic feet, so a cubic yard (27 cubic feet) takes 45 of them. A 60 lb bag makes 0.45 cubic feet (60 per yard), a 50 lb bag 0.375 (72 per yard) and a 40 lb bag 0.30 (90 per yard). The calculator turns the volume of your pour into whole bags in every size, then adds the water and the mixing it takes.
How the number of bags is calculated
Work out the volume in cubic feet, add the waste allowance, divide by what one bag yields, and round up: you cannot buy part of a bag.
Bags = volume (cu ft) × (1 + waste %) ÷ yield per bag (cu ft), rounded up
The yields come from the manufacturers' technical data sheets, not from rules of thumb:
| Bag | Yield | Bags per cubic yard | Source |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 | Quikrete 1101, Sakrete High-Strength |
| 50 lb | 0.375 cu ft | 72 | Quikrete 1101 |
| 60 lb | 0.45 cu ft | 60 | Quikrete 1101, Sakrete High-Strength |
| 80 lb | 0.60 cu ft | 45 | Quikrete 1101, Sakrete High-Strength |
| 90 lb | 0.675 cu ft | 40 | Quikrete 1101 (regional) |
Quikrete Fast-Setting Concrete Mix, the one often dry-poured into post holes, yields 0.375 cu ft per 50 lb bag and 0.45 per 60 lb bag, the same as the regular mix of those weights. Both are in the bag size list.
How many 80 lb bags of concrete are in a yard?
A cubic yard takes 45 bags of 80 lb concrete mix. One 80 lb bag makes 0.60 cubic feet (Quikrete Concrete Mix 1101; Sakrete High-Strength gives the same), and a yard is 27 cubic feet, so 27 ÷ 0.60 = 45. With the 10% allowance most pours need, that is 50 bags to buy. The other sizes follow from their own yields:
| Bag | Yield per bag | Bags per cu yd | Bags per ½ cu yd | Bags per ¼ cu yd | Dry weight per cu yd |
|---|---|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 | 45 | 23 | 3,600 lb |
| 50 lb | 0.375 cu ft | 72 | 36 | 18 | 3,600 lb |
| 60 lb | 0.45 cu ft | 60 | 30 | 15 | 3,600 lb |
| 80 lb | 0.60 cu ft | 45 | 23 | 12 | 3,600 lb |
Rounded up to whole bags at the fraction shown, no allowance. The dry weight is the same in every size because the concrete in the bag is the same; add the 10% and it is about 4,000 lb to carry per yard.
How many bags of concrete make a yard
The answer depends on the bag: 45 of 80 lb, 60 of 60 lb, 72 of 50 lb or 90 of 40 lb make one cubic yard (and 40 of the regional 90 lb bag, at 0.675 cu ft). That is why the concrete yard calculator matters as the pour grows: around a yard, bags mean 45 lifts of 80 lb and about 1.8 tons of dry mix in the truck, and an NRMCA mixer truck carries 8 to 12 cubic yards. To run the numbers for your pour, enter its size above and read the "Bags by size" table, which repeats this arithmetic with your volume, waste and price.
How many bags of concrete for a 10x10 slab
A 10 × 10 ft slab 4 inches thick is 10 × 10 × 4 ÷ 12 = 33.33 cubic feet. Without any allowance that is 56 bags of 80 lb, 75 of 60 lb, 89 of 50 lb or 112 of 40 lb. With the default 10% extra, the calculator's answer on load, it is 36.67 cubic feet:
- 62 bags of 80 lb
- 82 bags of 60 lb
- 98 bags of 50 lb
- 123 bags of 40 lb
Each size weighs about 4,900 lb in total, because a cubic foot of mixed concrete weighs about the same whatever bag it came in. Quikrete gives the unit weight of its mix as approximately 140 lb per cubic foot.
Bags for common slab sizes at 4 inches
With 10% extra, rounded up per size:
| Slab | Concrete | 80 lb | 60 lb | 50 lb | 40 lb |
|---|---|---|---|---|---|
| 4 × 4 ft | 5.87 cu ft | 10 | 14 | 16 | 20 |
| 4 × 8 ft | 11.73 cu ft | 20 | 27 | 32 | 40 |
| 8 × 8 ft | 23.47 cu ft | 40 | 53 | 63 | 79 |
| 10 × 10 ft | 36.67 cu ft | 62 | 82 | 98 | 123 |
| 10 × 12 ft | 44 cu ft | 74 | 98 | 118 | 147 |
| 12 × 12 ft | 52.8 cu ft | 88 | 118 | 141 | 176 |
For post holes and sonotubes, the sonotube concrete calculator gives bags per hole with the post subtracted.
Water to mix the bags
Quikrete's data sheet gives a starting and a maximum amount of water per bag: 6 to 9 pints for an 80 lb bag, 4 to 7 for 60 lb, 3½ to 5½ for 50 lb and 3 to 4½ for 40 lb. Sakrete lists 3½ quarts (7 pints) for its 80 lb bag. For the 62 bags of the 10 × 10 example that is 47 to 70 gallons. Start low and add water only until the mix is stiff but workable: both manufacturers warn that extra water lowers strength.
Quikrete also says to allow at least 1 cubic foot of mixer drum per 80 lb bag. In a mixer with a 3 cubic foot drum that is three 80 lb bags a batch, so the 62 bags take 21 batches. At that point, weigh the work against a truck.
40, 60 or 80 lb bags
The concrete inside is the same, so choose by what you can lift and pour. 80 lb bags mean the fewest trips and tears; 40 and 50 lb bags suit steps, repairs and anyone lifting alone, at the cost of more bags and more packaging. Enter a price per bag and the calculator shows the total for the size you picked, so you can compare store prices per cubic foot.
When bags stop making sense
Past about a cubic yard, the concrete yard calculator is worth a look: a mixer truck carries 8 to 12 cubic yards (NRMCA), and even with a short-load fee it can beat 45 bags a yard in cost and effort. The concrete cost calculator compares the two for your state, and the concrete calculator handles every shape, including several at once. For a slab with a price, use the concrete slab calculator.