Concrete Calculator
Enter your project dimensions to estimate how much concrete you need — in cubic yards, cubic meters, and number of bags.
Fill in your dimensions and click Calculate to see your concrete estimate.
How to Calculate Concrete for Your Project
Concrete is sold by the cubic yard in the United States. To find out how many cubic yards you need, multiply the length, width, and thickness of your slab (all in feet), then divide by 27. Always add a 10% waste factor to account for spillage, uneven ground, and overpour.
Quick Reference: Cubic Yards by Slab Thickness
For a 10 ft × 10 ft area, here is how many cubic yards you need at different thicknesses:
- 2 inches thick: 0.62 yd³ (about 19 × 60 lb bags)
- 4 inches thick: 1.23 yd³ (about 37 × 60 lb bags)
- 6 inches thick: 1.85 yd³ (about 56 × 60 lb bags)
When to Order Ready-Mix vs. Buy Bags
For projects under 1 cubic yard, bagged concrete mix is usually more practical. For anything above 1 yard, ordering ready-mix concrete from a local supplier is more cost-effective and less labor-intensive. Most ready-mix trucks carry a minimum of 1 yard.
Bag Sizes Explained
Concrete bags come in 40 lb, 60 lb, and 80 lb sizes. An 80 lb bag yields approximately 0.60 cubic feet of concrete. A 60 lb bag yields about 0.45 cubic feet, and a 40 lb bag yields about 0.30 cubic feet. This calculator automatically converts your volume into bag counts for all three sizes.
Building Stairs Instead of a Slab?
If your project is a full staircase rather than a simple set of steps, especially one with a landing at the top, our dedicated Concrete Stairs Calculator walks through each step individually and adds the landing volume automatically, with no need to understand stacking formulas by hand.