Concrete Calculator — Cubic Yards & Bags
Enter your slab or pad's length, width, and depth to get the concrete you need in cubic yards, cubic feet, and bags. No sign-up, no data stored.
Concrete needed
How concrete volume is calculated
The math is straightforward:
- Volume = length × width × depth (all in the same unit).
- In feet: depth in inches ÷ 12. A 4-inch slab = 4 ÷ 12 = 0.333 ft.
- Cubic yards = cubic feet ÷ 27 (there are 27 cu ft in a cubic yard).
- Bags = cubic feet ÷ bag yield, rounded up. Standard yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft.
We add your selected waste percentage to the total before computing bags, so you won't run short mid-pour.
Concrete reference chart
Bag yields and typical slab depths.
Bag mix yields
| Bag size | Yields |
|---|---|
| 40 lb | ≈ 0.30 cu ft |
| 60 lb | ≈ 0.45 cu ft |
| 80 lb | ≈ 0.60 cu ft |
Typical slab depths
| Project | Depth |
|---|---|
| Patio / walkway | 4 in |
| Driveway | 4–6 in |
| Shed / garage floor | 4 in |
| Footings | check local code |
Last updated: October 2026 · 1 cu yd = 27 cu ft. Bag yields are standard manufacturer values (Quikrete, Sakrete, etc.).
Concrete calculator FAQ
A 10×10 ft slab 4 inches deep is ~33.3 cu ft. That's about 56 bags of 80 lb (33.3 ÷ 0.60 ≈ 55.6), or about 74 bags of 60 lb.
27 cubic feet in one cubic yard. Divide your cubic feet by 27 to get cubic yards — what most ready-mix suppliers quote.
For projects under about 1 cubic yard, bags are usually easier and cheaper. For larger slabs, ordering a ready-mix truck is more practical and cost-effective.
A 4×4 ft pad 4 inches deep is 5.33 cu ft — about 9 bags of 80 lb (5.33 ÷ 0.60 ≈ 8.9), or 12 bags of 60 lb.
Yes — add about 10% for spillage and uneven ground. It's far better to have a little extra than to run short mid-pour.