Concrete Calculator
Enter the slab size in feet and the thickness in inches. Patios and walkways are usually 4 inches thick; driveways 4–6 inches.
ft
ft
in
$
Ready-mix trucks often have a minimum order; bags are usually cheaper below about 1 cubic yard.
Result–
Concrete for common slab sizes
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 10 × 10 ft × 4 in | 1.23 | 62 | 82 |
| 10 × 12 ft × 4 in | 1.48 | 74 | 98 |
| 12 × 12 ft × 4 in | 1.78 | 89 | 118 |
| 12 × 20 ft × 4 in | 2.96 | 147 | 196 |
| 20 × 20 ft × 4 in | 4.94 | 245 | 326 |
| 24 × 24 ft × 4 in | 7.11 | 353 | 470 |
| 10 × 10 ft × 6 in | 1.85 | 92 | 123 |
| 20 × 20 ft × 6 in | 7.41 | 367 | 489 |
Bag counts include 10% extra. An 80 lb bag makes about 0.6 cu ft; a 60 lb bag about 0.45 cu ft.
Cubic yards = length × width × (thickness in inches ÷ 12) ÷ 27
Questions
How many bags of concrete for a 10 × 10 slab?
At 4 inches thick, about 1.23 cubic yards: roughly 62 bags of 80 lb concrete with 10% extra.
How many 80 lb bags make a yard of concrete?
About 45 bags (27 cu ft ÷ 0.6 cu ft per bag).
How thick should a concrete slab be?
4 inches for patios and walkways, 5–6 inches for driveways and heavier loads.