Shops sell concrete two ways: by the cubic yard from a truck, and in bags. This page changes one into the other, so you can compare prices and plan any job.
One cubic yard = 45 bags of 80 lb concrete mix.
Step 1: One cubic yard is 27 cubic feet (3 ft × 3 ft × 3 ft).
Step 2: One 80 lb bag of mix makes about 0.6 cubic feet of finished concrete, it is printed on the bag.
Step 3: Divide: 27 ÷ 0.6 = 45 bags. That is the whole trick, every bag size works the same way, just divide 27 by what one bag makes.
| Bag size | One bag makes | Bags in 1 cubic yard |
|---|---|---|
| 40 lb | 0.3 cu ft | 90 bags |
| 60 lb | 0.45 cu ft | 60 bags |
| 80 lb | 0.6 cu ft | 45 bags |
And for amounts, in 80 lb bags: ¼ yard = 12 bags · ½ yard = 23 bags · 1 yard = 45 bags · 2 yards = 90 bags · 3 yards = 135 bags (rounded up, bags are sold whole).
Because the count follows the finished volume, not the weight. A 40 lb bag makes half as much concrete as an 80 lb bag (0.3 vs 0.6 cu ft), so you need twice as many.
After mixing, it is the finished concrete one bag makes with water added, the number printed on the bag. All our calculators use that same number.
62 bags at 4 inches thick, including the 10% safety extra. The full working is on our 10×10 slab guide.