How Much Does a Concrete Slab Cost? Bags vs Ready-Mix
The cost of a slab starts with its volume. A slab 20 × 10 ft and 4 in thick needs 2.72 cubic yards with 10% extra, which is 123 bags of 80 lb. The concrete cost calculator then multiplies by your own prices for bags and for ready-mix.
Part of the project planner: Planning a concrete patio, slab or driveway.
Yards and bags for common slabs
4 in thick, with 10% extra.
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 10 × 10 ft | 1.36 | 62 | 82 |
| 12 × 12 ft | 1.96 | 88 | 118 |
| 20 × 10 ft | 2.72 | 123 | 163 |
| 20 × 20 ft | 5.43 | 245 | 326 |
| 24 × 24 ft | 7.82 | 352 | 470 |
| 30 × 30 ft | 12.22 | 550 | 734 |
How the thickness changes it
For a slab of 20 × 10 ft:
| Thickness | Cubic yards | 80 lb bags |
|---|---|---|
| 3.5 in | 2.38 | 107 |
| 4 in | 2.72 | 123 |
| 5 in | 3.40 | 153 |
| 6 in | 4.07 | 184 |
Bags or ready-mix?
- Bags. No delivery fee and you can work in stages, but each bag is mixed by hand, and the price for each yard is higher.
- Ready-mix. A lower price for each yard, but a delivery fee, often a charge for a small load, and a crew that must place and finish it quickly.
- The break-even. Often between 1 and 2 cubic yards. Get a quote and put it in the calculator.
What the price does not include
- The gravel base, the forms and the reinforcing mesh or rebar.
- The tools, such as floats, edgers and a mixer.
- The labor, if you do not do it yourself.
- The removal of old concrete or soil, and a permit if your area needs one.
See also the concrete calculator and the concrete slab materials calculator. These are estimates: the prices are yours.
Frequently asked questions
How much does a concrete slab cost?
It is the volume times the price, plus the base and the labor. A slab of 200 sq ft at 4 in is 2.72 cubic yards with 10% extra.
Are bags cheaper than ready-mix?
For a small job, usually. Ready-mix wins as the volume rises, because its delivery fee is spread over more yards. Put your own prices in the calculator.
How many bags make a cubic yard?
About 45 bags of 80 lb, or 60 bags of 60 lb, since the bags yield 0.6 and 0.45 cubic feet and a yard is 27 cubic feet.
How much extra should I order?
About 10%, for the uneven ground and the spillage. Running short in the middle of a pour is costly.
What is not in the price?
The base, the forms, the reinforcing, the tools, the finishing and any labor.
More guides
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.