Concrete slab calculator
Enter the finished length, width and thickness. See exactly how the slab volume turns into cubic yards and bags.
Enter slab dimensions
How to calculate concrete for a slab
Multiply length × width × thickness, using the same unit for every dimension. When length and width are in feet and thickness is in inches, divide thickness by 12 to get feet. Divide cubic feet by 27 for cubic yards. Multiply by the number of identical slabs, then apply your chosen waste percentage.
Formula: (length in ft × width in ft × thickness in ÷ 12 × quantity) ÷ 27 = exact yd³.
Worked example: a 10 × 10 ft slab, 4 in thick
10 × 10 × (4 ÷ 12) = 33.33 ft³. That is 1.235 yd³ before extra. With 10% waste, the order estimate is 1.358 yd³, displayed as 1.36 yd³. At 0.60 ft³ per 80 lb bag, 36.67 ÷ 0.60 = 61.11, so round up to 62 bags.
Common square slab sizes at 4 inches
These are material quantities for one rectangular slab, using 10% extra and an example 0.60 ft³ yield per 80 lb bag. Confirm the finished dimensions and your chosen bag label.
| Slab size | Thickness | Exact | With 10% extra | Bags |
|---|---|---|---|---|
| 8 × 8 ft | 4 in | 0.79 yd³ | 0.87 yd³ | 40 × 80 lb |
| 10 × 10 ft | 4 in | 1.23 yd³ | 1.36 yd³ | 62 × 80 lb |
| 12 × 12 ft | 4 in | 1.78 yd³ | 1.96 yd³ | 88 × 80 lb |
| 20 × 20 ft | 4 in | 4.94 yd³ | 5.43 yd³ | 245 × 80 lb |
| 24 × 24 ft | 4 in | 7.11 yd³ | 7.82 yd³ | 352 × 80 lb |
How much for a 10 × 10 ft slab?
At 4 in: 1.23 yd³ exact, 1.36 yd³ with 10% extra. At 5 in: 1.54 yd³ exact, 1.70 yd³ with 10% extra. At 6 in: 1.85 yd³ exact, 2.04 yd³ with 10% extra. These are quantity comparisons, not thickness recommendations.
What this estimate does not decide
This is a material volume estimate. It does not determine structural thickness, reinforcement, ground preparation, joint spacing, delivery minimums or finishing labor. Use the finished pour dimensions and ask a qualified professional about structural design.
Questions people ask
How many yards are in a 10 × 10 slab at 4 inches?
About 1.23 yd³ exact, or 1.36 yd³ with 10% extra.
Can I add multiple slabs?
Use the number-of-slabs field for identical slabs. For different sizes, use the multi-pour calculator.
Content and calculator by pourmeasure. Formula and assumption notes: methodology and sources. Updated October 2026. No independent engineering review is claimed.