Concrete Calculator
Calculate how much concrete you need for slabs, footings, and posts in cubic yards and bags.
ft
ft
in
$
Concrete Needed
1.23 yd³
56 bags (80lb)
How to Calculate Concrete
Cubic Feet = Length(ft) × Width(ft) × Depth(in)/12
Cubic Yards = Cubic Feet ÷ 27
Bags = Cubic Feet ÷ 0.6 (per 80lb bag)
Cubic Yards = Cubic Feet ÷ 27
Bags = Cubic Feet ÷ 0.6 (per 80lb bag)
Concrete Bag Coverage
| Bag Size | Cubic Feet per Bag | Bags per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
Common Concrete Projects
| Project | Typical Size | Concrete Needed |
|---|---|---|
| Patio slab | 10×10 ft, 4" thick | 1.23 yd³ |
| Driveway | 20×20 ft, 6" thick | 7.41 yd³ |
| Sidewalk | 4×20 ft, 4" thick | 0.99 yd³ |
| Post footing | 12" dia × 24" deep | 0.16 yd³ |
Frequently Asked Questions
How do I calculate how much concrete I need?
Multiply length × width × depth to get cubic volume. For a 10ft × 10ft slab that's 4 inches deep: 10 × 10 × (4/12) = 33.3 cubic feet = 1.23 cubic yards. Order 5-10% extra for waste.
How many bags of concrete equal 1 cubic yard?
It takes about 45 bags of 80lb concrete mix to make 1 cubic yard, or 60 bags of 60lb mix. Each 80lb bag yields about 0.6 cubic feet.
How thick should a concrete slab be?
Patios and walkways: 4 inches. Driveways: 4–6 inches. Foundations: 8–12 inches. Always check local building codes for minimum thickness requirements.
How much does concrete cost?
Ready-mix concrete costs $100–$150 per cubic yard (plus delivery). Bagged concrete (DIY) costs $4–$7 per 80lb bag. A typical 10×10 patio slab needs about 1.5 yards ($150–$225).