Concrete Calculator
Concrete for a slab: cubic yards to order, or how many 80 lb and 60 lb bags to buy.
- Volume (cubic feet)33.3
- Volume (cubic yards)1.23
- 80 lb bags (≈0.6 cu ft each)56
- 60 lb bags (≈0.45 cu ft each)75
Inputs used
- Length10 ft
- Width10 ft
- Thickness4 in
About this calculator
A slab's volume is length × width × thickness — with thickness converted from inches to feet first. A 10 × 10 ft patio at 4 inches thick needs 10 × 10 × ⅓ ≈ 33.3 cubic feet, which is about 1.23 cubic yards (there are 27 cubic feet in a cubic yard).
Ready-mix trucks sell by the cubic yard; for small jobs, bagged mix works: an 80 lb bag yields about 0.6 cubic feet and a 60 lb bag about 0.45. The bag counts below round up, but order roughly 10% extra on top — uneven ground and spillage always eat some, and running short mid-pour is the one mistake you can't fix later.
Standard slab thicknesses: 4 inches for patios and walkways, 5–6 inches for driveways.
Quick reference
Cubic yards of concrete by slab size — 4 inch thick
Concrete volume in cubic yards for a 4-inch-thick slab, by length and width in feet.
| Length | 8 ft | 10 ft | 12 ft | 16 ft | 20 ft |
|---|---|---|---|---|---|
| 8 ft | 0.79 | 0.99 | 1.19 | 1.58 | 1.98 |
| 10 ft | 0.99 | 1.23 | 1.48 | 1.98 | 2.47 |
| 12 ft | 1.19 | 1.48 | 1.78 | 2.37 | 2.96 |
| 16 ft | 1.58 | 1.98 | 2.37 | 3.16 | 3.95 |
| 20 ft | 1.98 | 2.47 | 2.96 | 3.95 | 4.94 |
| 24 ft | 2.37 | 2.96 | 3.56 | 4.74 | 5.93 |
80 lb concrete bags by slab size — 4 inch thick
Number of 80 lb bags (≈0.6 cu ft each) for a 4-inch-thick slab, by length and width in feet.
| Length | 8 ft | 10 ft | 12 ft | 16 ft | 20 ft |
|---|---|---|---|---|---|
| 8 ft | 36 | 45 | 54 | 72 | 89 |
| 10 ft | 45 | 56 | 67 | 89 | 112 |
| 12 ft | 54 | 67 | 80 | 107 | 134 |
| 16 ft | 72 | 89 | 107 | 143 | 178 |
| 20 ft | 89 | 112 | 134 | 178 | 223 |
| 24 ft | 107 | 134 | 160 | 214 | 267 |
Frequently asked questions
How many 80 lb bags of concrete do I need for a 10x10 slab?
A 10 × 10 ft slab at 4 inches thick is about 33.3 cubic feet, and each 80 lb bag yields roughly 0.6 cubic feet, so you need 56 bags. Order about 10% extra to cover spillage and uneven ground.
How many cubic yards of concrete for a 10x10 slab?
At 4 inches thick, a 10 × 10 ft slab is about 1.23 cubic yards (33.3 cubic feet divided by 27). At 6 inches it rises to about 1.85 cubic yards.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet. At about 0.6 cubic feet per 80 lb bag that is 45 bags, or 60 bags of 60 lb mix (≈0.45 cubic feet each) — which is why ready-mix is far cheaper once a job runs past a yard or so.
How thick should a concrete slab be?
Four inches is standard for patios, walkways and shed floors; driveways and anything carrying vehicle weight are usually poured 5 to 6 inches thick, often over a compacted gravel base.
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