Concrete Calculator
Estimate the volume of concrete needed for your pouring project. Enter the dimensions in feet to get the result in cubic feet and cubic yards.
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Results
Enter dimensions and click calculate to see the volume needed.
Formula Explanation
Concrete is usually ordered in cubic yards. First we find the cubic feet, then divide by 27 (since 1 cubic yard = 27 cubic feet):
Note: It's often recommended to add 5-10% to your final estimate to account for spills, uneven subgrades, and waste.
Understanding Concrete Volume
Concrete for large projects — driveways, foundations, slabs — is ordered in cubic yards from a ready-mix supplier. For smaller DIY jobs, pre-mixed bags of concrete (40 lb, 60 lb, or 80 lb) are the practical option. Knowing how much you need before you start prevents costly over-ordering or frustrating mid-job shortages.
A standard 80 lb bag of concrete mix yields approximately 0.60 cubic feet of cured concrete. A 60 lb bag yields about 0.45 cubic feet, and a 40 lb bag yields roughly 0.30 cubic feet. Always add 5–10% extra to your estimate to account for spills, uneven sub-grades, and waste.
Bag Size Reference
| Bag Size | Yield (cubic feet) | Best For |
|---|---|---|
| 40 lb | ~0.30 cu ft | Small repairs, posts |
| 60 lb | ~0.45 cu ft | Medium projects |
| 80 lb | ~0.60 cu ft | Slabs, driveways, foundations |
How to Use This Calculator
- Enter the length and width of the area to be poured, in feet.
- Enter the depth in feet (e.g., 6 inches = 0.5 ft, 4 inches ≈ 0.33 ft).
- Select the bag size you plan to use from the dropdown.
- Click Calculate to see cubic feet, cubic yards, and the number of bags needed.
Frequently Asked Questions
How thick should a concrete slab be?
A standard residential concrete slab is 4 inches thick (0.33 ft). Driveways that will support vehicle traffic are typically poured at 6 inches (0.5 ft). Sidewalks and pathways for foot traffic are commonly 4 inches. Structural foundations are 8 inches or more and should be designed by an engineer.
When should I order ready-mix instead of using bags?
Ready-mix concrete from a truck becomes more economical at around 1 cubic yard or more (about 45 bags). For smaller pours, pre-mixed bags give you more control over timing and are easier to handle without specialized equipment.
Why should I add extra concrete to my estimate?
Always add 5–10% to the calculated volume as a buffer. Sub-grades are rarely perfectly level, forms can flex slightly, and mixing waste is unavoidable. Running short mid-pour creates cold joints that weaken the finished slab.