Concrete Calculator
Updated Formulas shown
Enter the slab size and thickness. The calculator gives you the volume in cubic yards (what ready-mix plants sell), the number of pre-mixed bags, and the cost. A 10 × 10 ft patio at 4 inches needs about 1.23 cubic yards, or 56 bags of 80 lb before waste.
- 80 lb bags
- 620.6 ft³ each
- 80 lb bags
- 62
- 60 lb bags
- 82
- Cubic feet
- 36.67 ft³
- Cubic meters
- 1.04 m³
- Weight (wet)
- 5,500 lb
Includes your waste allowance. Bag yields: 40 lb = 0.30 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³.
How to use it
- Measure length and width in feet. For L-shapes, split into rectangles and add them up.
- Pick a thickness: 4 in for patios, sidewalks and shed floors; 5–6 in for driveways and garage slabs.
- Keep 5–10% extra for uneven subgrade and spillage.
- Under ~1 yd³ use bags; above that, compare against a ready-mix delivery (most plants have a short-load fee under 3–4 yd³).
The formula
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. Bags = cubic feet ÷ bag yield (0.60 ft³ for an 80 lb bag, 0.45 for 60 lb, 0.30 for 40 lb).
Quick reference
| Slab size | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 4 × 4 ft | 0.2 | 5.3 | 9 | 12 | 18 |
| 8 × 8 ft | 0.79 | 21.3 | 36 | 48 | 72 |
| 10 × 10 ft | 1.23 | 33.3 | 56 | 75 | 112 |
| 10 × 12 ft | 1.48 | 40 | 67 | 89 | 134 |
| 10 × 20 ft | 2.47 | 66.7 | 112 | 149 | 223 |
| 12 × 12 ft | 1.78 | 48 | 80 | 107 | 160 |
| 12 × 16 ft | 2.37 | 64 | 107 | 143 | 214 |
| 12 × 20 ft | 2.96 | 80 | 134 | 178 | 267 |
| 16 × 16 ft | 3.16 | 85.3 | 143 | 190 | 285 |
| 20 × 20 ft | 4.94 | 133.3 | 223 | 297 | 445 |
| 20 × 24 ft | 5.93 | 160 | 267 | 356 | 534 |
| 24 × 24 ft | 7.11 | 192 | 320 | 427 | 640 |
| 30 × 30 ft | 11.11 | 300 | 500 | 667 | 1000 |
Related calculators
- Concrete Slab Cost CalculatorEstimate the cost of a concrete slab, patio or driveway: material per cubic yard plus labor per square foot, with 2026 US price ranges.
- Concrete Bag CalculatorHow many bags of concrete do you need? Enter the size of your slab or pad to get the exact number of 40, 60 and 80 lb bags of Quikrete or Sakrete.
- Concrete Footing CalculatorCalculate concrete for continuous wall footings: enter total length, width and depth to get cubic yards and bags.
- Rebar CalculatorCalculate rebar for a concrete slab: bars each way, total linear feet and 20 ft pieces including laps.
- Gravel CalculatorHow much gravel do you need? Enter area and depth to get cubic yards and tons, with cost per ton.
Frequently asked questions
How many bags of concrete do I need for a 10x10 slab?
At 4 inches thick, a 10 × 10 slab is 33.3 cubic feet (1.23 yd³): 56 bags of 80 lb, 75 bags of 60 lb or 112 bags of 40 lb. Add 5–10% for waste.
How much does a yard of concrete cost?
In 2026 most US ready-mix plants charge about $150–$200 per cubic yard delivered, plus short-load fees for small orders. Bagged concrete works out to roughly $250–$350 per yard.
How thick should a concrete slab be?
4 inches for patios, walkways and sheds; 5–6 inches with rebar or wire mesh for driveways and anything carrying vehicles.
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Estimates only. Check quantities with your supplier or contractor before ordering.