Estimate how many cubic yards of concrete you need for slabs, pads, sidewalks, driveways, footings, and flatwork.
A 20 ft × 20 ft slab at 4 inches thick requires approximately 4.9 cubic yards before waste, or about 5.4 cubic yards with 10% waste.
The basic concrete yardage formula is:
Cubic yards = length × width × thickness in feet ÷ 27
Because concrete thickness is usually entered in inches, divide the thickness by 12 first. Then multiply length, width, and thickness in feet to get cubic feet. Finally, divide by 27 to convert cubic feet into cubic yards.
For a 20 ft × 20 ft slab at 4 inches thick:
These estimates do not include waste unless noted. Add 5% to 10% overage for many real-world pours.
| Slab size | 4 inches thick | 5 inches thick | 6 inches thick |
|---|---|---|---|
| 10 ft × 10 ft | 1.2 cu yd | 1.5 cu yd | 1.9 cu yd |
| 20 ft × 20 ft | 4.9 cu yd | 6.2 cu yd | 7.4 cu yd |
| 24 ft × 24 ft | 7.1 cu yd | 8.9 cu yd | 10.7 cu yd |
| 30 ft × 40 ft | 14.8 cu yd | 18.5 cu yd | 22.2 cu yd |
| 50 ft × 100 ft | 61.7 cu yd | 77.2 cu yd | 92.6 cu yd |
This calculator provides estimates only. Actual concrete quantities may vary based on field measurements, formwork, subgrade conditions, slab thickness, reinforcement, waste, supplier batching, and project specifications. Always confirm final quantities with project plans, specifications, supplier, engineer, or qualified professional before ordering concrete or bidding work.