Worked example: 24 × 24 ft at 4 inches
| Step | Math | Result |
|---|---|---|
| Area | 24 ft × 24 ft | 576 sq ft |
| Volume at 4 in | 576 sq ft × 4 in ÷ 12 | 192.0 ft³ |
| Add 10% extra | 192.0 × 1.10 | 211.2 ft³ |
| Cubic yards | 211.2 ÷ 27 | 7.82 yd³ |
| 80 lb bags | 211.2 ÷ 0.60, rounded up | 352 bags |
| 60 lb bags | 211.2 ÷ 0.45, rounded up | 470 bags |
| 40 lb bags | 211.2 ÷ 0.30, rounded up | 704 bags |
Yards and bags at 4, 5 and 6 inches
| Thickness | Cubic feet (+10%) | Cubic yards (+10%) | 80 lb bags | 60 lb bags | 40 lb bags | Ready-mix order (yd³) |
|---|---|---|---|---|---|---|
| 4 in | 211.2 | 7.82 | 352 | 470 | 704 | 8.00 |
| 5 in | 264.0 | 9.78 | 440 | 587 | 880 | 10.00 |
| 6 in | 316.8 | 11.73 | 528 | 704 | 1056 | 11.75 |
Bags vs ready-mix cost
| Thickness | 80 lb bags | 60 lb bags | 40 lb bags | Ready-mix | Cheaper (80 lb) |
|---|---|---|---|---|---|
| 4 in | $2,288 | $2,468 | $2,992 | $1,360 | Ready-mix |
| 5 in | $2,860 | $3,082 | $3,740 | $1,700 | Ready-mix |
| 6 in | $3,432 | $3,696 | $4,488 | $1,998 | Ready-mix |
For the 4 in slab, ready-mix is cheaper by about $928 and avoids mixing 352 bags (28,160 lb) by hand. At 8.00 yd³ you clear the typical 4 yd³ short-load threshold, so no short-load fee applies.
Prices used: 80 lb bag $6.50, 60 lb $5.25, 40 lb $4.25; ready-mix $170/yd³ with a $150 short-load fee under 4 yd³ (orders are rounded up to ¼ yd³, 1 yd³ minimum). Local prices vary a lot; change them in the calculator.
Planning notes for 24 × 24 ft
- Truck access: one truck holds this pour in a single load. Chutes reach about 15–20 ft; farther than that you need wheelbarrows or a pump.
- Weight: the 4 in pour weighs about 15.6 tons. Bags alone weigh 28,160 lb at 80 lb each.
- Gravel base: a 4 in compacted gravel base under this slab takes about 10.9 tons (7.8 yd³) with 10% extra. See gravel for a driveway.
- Thickness: 4 in suits patios, sheds and walks; 5–6 in is common for vehicle loads. See how thick a slab should be.
Nearby sizes
Also see 20×24 slab , 30×30 slab , 20×20 slab, or the full slab chart. For other sizes, open the concrete calculator, or compare bags and ready-mix.