How to Calculate Concrete Volume
Concrete volume is calculated by multiplying the length × width × depth (for slabs) or π × radius² × depth (for cylinders). The result in cubic feet is then converted to cubic yards (÷27) for ordering ready-mix concrete from a supplier.
Concrete Formulas
Slab / Footing:
Volume (ft³) = length × width × (thickness_in / 12)
Cubic Yards = ft³ / 27
Column / Cylinder:
Volume (ft³) = π × (diameter_in/24)² × depth_ft
Cubic Yards = ft³ / 27
Bags needed = ft³ / bag_volume_ft³
Standard Concrete Thicknesses
| Application | Recommended Thickness |
|---|---|
| Sidewalk / Patio | 4 inches |
| Driveway (residential) | 4–6 inches |
| Garage floor | 4–6 inches |
| Foundation wall footing | 8–12 inches |
| Steps | 3.5 inches per step |
| Post hole (diameter) | 3× post width |
Tips for Ordering Concrete
Always order 5–10% more concrete than your calculated volume to account for spillage, uneven ground, and overfill. For small projects under 0.5 cubic yards, pre-mixed bags are cost-effective. For larger projects, ready-mix delivery (sold by the cubic yard) is more economical and time-efficient. Most ready-mix suppliers have a minimum order of 1 cubic yard.