Bags of concrete calculator
Enter your measurements and pick a bag size. See how many bags to buy.
How the bag count is worked out
The calculator finds the volume you need in cubic feet, adds your extra percentage, and divides by what one bag yields. It rounds up, since you cannot buy part of a bag. The yields are the manufacturer's: 0.6 cubic feet for an 80 lb bag, 0.45 for 60 lb, 0.375 for 50 lb and 0.3 for 40 lb (Quikrete data sheet).
| Bag size | Yield per bag | Bags per cubic yard | Bags per cubic yard, with 10% extra |
|---|---|---|---|
| 80 lb bag | 0.6 cu ft | 45 | 50 |
| 60 lb bag | 0.45 cu ft | 60 | 66 |
| 50 lb bag | 0.375 cu ft | 72 | 80 |
| 40 lb bag | 0.3 cu ft | 90 | 99 |
Example: a 10 x 10 ft slab, 4 inches thick
The slab needs 33.33 cubic feet. With 10% extra that is 36.67 cubic feet, which takes 62 bags of 80 lb mix, 82 bags of 60 lb mix, 98 bags of 50 lb mix or 123 bags of 40 lb mix.
| Job | Volume | Order with 10% extra | 80 lb bags |
|---|---|---|---|
| Fence post hole, 10 in wide, 30 in deep | 1.36 cu ft | 0.06 cu yd | 3 |
| Deck footing, 12 in wide, 42 in deep | 2.75 cu ft | 0.11 cu yd | 6 |
| 4 x 4 ft pad, 4 in thick | 5.33 cu ft | 0.22 cu yd | 10 |
| Footing 40 ft long, 16 in wide, 8 in deep | 35.56 cu ft | 1.45 cu yd | 66 |
When bags stop making sense
Mixing a large number of bags by hand is slow, and batches that dry at different times can leave visible joints. Many people switch to ready-mix when the job passes a cubic yard or so. The concrete calculator gives the cubic yards to order. Yields vary a little by product and by how much water you add, so check the bag.
Questions people ask
How many 80 lb bags of concrete make a yard?
About 45. A cubic yard is 27 cubic feet, and an 80 lb bag yields about 0.60 cubic feet. See the full table in the guide to bags of concrete in a yard.
How many bags of concrete do I need for a post hole?
A 12 inch wide, 42 inch deep hole takes about 2.7 cubic feet, so about 6 bags of 80 lb mix with 10% extra.
Are the bag yields exact?
No. They are approximate, from the manufacturer. Different brands and mixes can differ a little. Check the label on the bag you buy.
Should I round up?
Yes. Running short mid-pour can leave a cold joint. The calculator rounds up and adds your extra percentage.