How Much Concrete Do You Need?
Concrete is ordered by the cubic yard. Over-ordering wastes hundreds of dollars; under-ordering means a cold joint and a weaker slab. This calculator gives you the exact cubic yards, bags, and estimated cost for slabs, footings, and columns.
The Concrete Volume Formula
The 27 divides cubic feet into cubic yards, the standard unit for ordering concrete.
Worked Example: 10 x 10 ft Slab, 4" Thick
- Length: 10 ft
- Width: 10 ft
- Depth: 4 inches = 0.333 ft
- Volume: (10 ร 10 ร 0.333) รท 27 = 1.23 cubic yards
- Order 1.5 yards (add 10% for spillage and uneven subgrade)
Bagged Concrete vs Ready-Mix
| Volume | Best Option |
|---|---|
| Under 1 cu yd | Bagged concrete (60-80 lb bags) |
| 1-3 cu yd | Ready-mix (minimum order usually 1 yd) |
| 3-10 cu yd | Ready-mix delivery |
| 10+ cu yd | Ready-mix, multiple trucks |
Bag math: 80 lb bag = 0.6 cu ft. 60 lb bag = 0.45 cu ft. 45 bags of 80 lb = 1 cu yd.
Common Concrete Projects
| Project | Typical Thickness |
|---|---|
| Patio / walkway | 4 inches |
| Driveway (cars) | 4-5 inches |
| Driveway (heavy trucks) | 6 inches |
| Garage slab | 4-6 inches |
| Footings | 6-12 inches |
| Shed base | 4 inches |
Cost Estimate (2026 US)
- Ready-mix concrete: $130-$180 per cubic yard
- Delivery fee: $50-$200
- Short load fee: $50-$100
- Bagged concrete: $4-$7 per 80 lb bag
- Finishing labor: $2-$5 per sq ft
Frequently Asked Questions
How many 80 lb bags of concrete in a yard?
45 bags of 80 lb make 1 cubic yard.
How much does a yard of concrete cover?
1 cubic yard covers 81 sq ft at 4 inches thick.
How thick should a driveway be?
4 inches for cars, 5-6 inches for trucks, RVs, or heavy loads.
How long before I can walk on new concrete?
24-48 hours for foot traffic, 7 days for vehicles, 28 days for full cure.
Do I need rebar in a slab?
For driveways and structural slabs, yes. Use #3 or #4 rebar on 12-24 inch centers.
What is the difference between concrete and cement?
Cement is one ingredient in concrete. Concrete = cement + sand + gravel + water.