Enter your project dimensions to calculate concrete volume
Concrete volume is calculated by multiplying length × width × depth. For a rectangular slab, the formula is straightforward: Volume = Length (ft) × Width (ft) × Depth (in) ÷ 12 ÷ 27. Dividing by 12 converts inches to feet, and dividing by 27 converts cubic feet to cubic yards — the standard ordering unit for ready-mix concrete.
| Project | Dimensions | Thickness | Cubic yards |
|---|---|---|---|
| Sidewalk | 4 ft × 20 ft | 4 in | 0.99 |
| Patio | 10 ft × 12 ft | 4 in | 1.48 |
| Driveway (single) | 10 ft × 20 ft | 4 in | 2.47 |
| Driveway (double) | 20 ft × 20 ft | 5 in | 6.17 |
| Garage floor | 20 ft × 24 ft | 4 in | 5.93 |
Concrete comes in two forms: pre-mixed bags (40, 60, or 80 lb bags you mix yourself) and ready-mix delivered by truck. For projects under 1 cubic yard, bags are practical. Over 1 yard, ready-mix delivery is more efficient and typically costs less per cubic yard. An 80 lb bag yields approximately 0.6 cubic feet, so one cubic yard requires about 45 bags of 80 lb mix.
Order 10% more concrete than your calculated volume. Subgrade irregularities, spillage, and slight over-excavation always consume more material than the mathematical calculation suggests. Running short mid-pour is far more problematic than having a small surplus.
| Application | Minimum thickness |
|---|---|
| Sidewalk (foot traffic) | 4 inches |
| Patio | 4 inches |
| Driveway (cars) | 4–5 inches |
| Driveway (heavy vehicles) | 5–6 inches |
| Garage floor | 4–6 inches |
| Foundation footing | 8–12 inches |
Divide the total volume in cubic feet by the bag yield: an 80 lb bag yields 0.6 cu ft, a 60 lb bag yields 0.45 cu ft, and a 40 lb bag yields 0.3 cu ft. Or use this calculator which does the conversion automatically.
Ready-mix concrete typically costs $125–$165 per cubic yard delivered, plus a delivery fee. Pre-mixed bags cost roughly $5–8 per 80 lb bag, which works out to about $250–$360 per cubic yard — significantly more expensive than ready-mix for larger projects.
Standard thickness is 4 inches for sidewalks and patios. Driveways should be 4–5 inches. Heavy vehicle areas need 5–6 inches. Always check local building codes for specific requirements in your area.
Rebar is recommended for driveways, structural slabs, and any slab over 4 inches thick. Wire mesh helps control cracking in thinner slabs like sidewalks and patios. Neither adds significant strength but both help distribute loads and control crack propagation.
Concrete reaches about 70% of its full strength in 7 days and 99% in 28 days. You can walk on it after 24–48 hours. Drive on it after 7 days. Do not place heavy loads for 28 days. Keep it moist during the first 7 days for optimal curing.