Complete Guide: How to Calculate Concrete for a Slab
A concrete calculator converts your slab's length, width, and thickness into the exact volume of concrete you need to order, whether from a ready-mix truck (measured in cubic yards) or as premixed bags. This free tool gives you results in cubic feet, cubic yards, and cubic meters, plus a bag count if you're using premix.
💡 Quick Summary
Volume = length × width × thickness (converted to consistent units). Ready-mix concrete is ordered by the cubic yard, while premixed bags list their expected yield in cubic feet on the packaging.
Premix Bag Yield Reference
| Bag Size | Approx. Yield |
|---|---|
| 80 lb bag | ~0.60 cu ft |
| 60 lb bag | ~0.45 cu ft |
| 40 lb bag | ~0.30 cu ft |
Step-by-Step Instructions
- Enter your slab's length and width in feet.
- Enter your slab thickness in inches.
- Select a premix bag size if you're buying bagged concrete rather than ready-mix.
- Click ⚡ Calculate Concrete Needed.
- Review your volume in cubic feet, yards, and meters, then use 📋 Copy Summary to save your results.
Tip: Ready-mix concrete suppliers typically have a minimum order (often 1 cubic yard), so very small projects are often more economical with premixed bags instead.