Concrete Calculator
Free concrete calculator for slabs and pads. Get cubic yards, number of 40, 60 or 80 lb bags, and estimated cost.
- Cubic yards
- 1.36
- Tons
- 2.75
- Cubic feet
- 36.7
- Area
- 100 sq ft
Bulk cost
$224
Before delivery and tax
Bagged
62 bags · $403
Advanced: material density
Default price is a typical U.S. figure ($135–$200 per cubic yard), reviewed November 2026. Prices vary by region; enter your supplier's price for an exact total.
Concrete for slabs is ordered by the cubic yard from a ready-mix plant, or mixed from bags for small jobs. Under about one yard, bags are usually cheaper; above that, ready-mix saves time and money.
This calculator adds 10% to cover uneven subgrade and spillage, which is standard practice.
How to calculate how much concrete you need
- Measure the length and width of the area in feet.
- Decide on depth in inches (see the depth guide below).
- Multiply length × width to get square feet.
- Multiply by depth ÷ 12 to get cubic feet, then divide by 27 for cubic yards.
Cubic yards = length × width × thickness (in) ÷ 12 ÷ 27, plus 10%. An 80 lb bag yields 0.60 cubic feet.
Recommended concrete depth
| Project | Depth |
|---|---|
| Patio or walkway | 4 in |
| Driveway | 4–6 in |
| Shed or garage floor | 4–6 in |
| Hot tub pad | 6 in |
How much concrete for common project sizes
Cubic yards needed before any waste allowance.
| Area | 2 in deep | 3 in deep | 4 in deep | 6 in deep |
|---|---|---|---|---|
| 10 × 10 ft | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ | 1.85 yd³ |
| 10 × 20 ft | 1.23 yd³ | 1.85 yd³ | 2.47 yd³ | 3.7 yd³ |
| 12 × 12 ft | 0.89 yd³ | 1.33 yd³ | 1.78 yd³ | 2.67 yd³ |
| 20 × 20 ft | 2.47 yd³ | 3.7 yd³ | 4.94 yd³ | 7.41 yd³ |
| 12 × 50 ft (driveway) | 3.7 yd³ | 5.56 yd³ | 7.41 yd³ | 11.11 yd³ |
| 500 sq ft | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ | 9.26 yd³ |
| 1,000 sq ft | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ | 18.52 yd³ |
Tips before you order
- Many ready-mix plants charge a short-load fee for orders under 4 to 5 yards.
- Concrete reaches most of its strength in about 28 days; you can usually walk on it after 24 to 48 hours.
- Use 6 inches and rebar for slabs that will carry vehicles or hot tubs.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
45 bags. Each 80 lb bag yields about 0.6 cubic feet, and a yard is 27 cubic feet.
How much does a yard of concrete weigh?
About 4,000 pounds, or roughly 2 tons.
How much concrete do I need for a 10x10 slab?
At 4 inches thick, a 10 by 10 slab needs about 1.23 cubic yards, or 1.36 yards with 10% extra.