Convert slab dimensions into cubic yards of concrete for pads, sidewalks, driveways, slabs, and general concrete pours.
A 20 ft × 20 ft slab at 4 inches thick is about 4.9 cubic yards before waste, or about 5.4 cubic yards with 10% waste.
Concrete is commonly ordered by the cubic yard. To estimate concrete, first calculate the area in square feet, convert the thickness from inches to feet, then divide the cubic feet by 27.
Cubic yards = length × width × thickness in feet ÷ 27
This calculator is designed for quick planning estimates. Enter your slab length, width, and thickness to estimate cubic yards. You can also add a waste percentage to account for ordinary field variation, form conditions, and ordering cushion.
Use this quick reference table as a rough planning guide. Actual quantities should always be confirmed with plans, project specifications, site measurements, supplier guidance, and qualified professionals.
| 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 |
Many ready-mix trucks are commonly planned around a 10 cubic yard capacity, but actual delivery capacity can vary by supplier, truck type, local rules, access, project conditions, and delivery requirements. Confirm truck capacity with your supplier before scheduling concrete.
This calculator provides estimates only. Actual concrete quantities can vary based on field measurements, formwork, subgrade conditions, slab thickness, reinforcement, waste, supplier batching, project specifications, weather, and site conditions. Always confirm final quantities before ordering concrete or bidding work.