How to use it
- Enter the slab length in feet.
- Enter the slab width in feet.
- Enter the slab thickness in inches.
- Get your concrete cubic yards, bag count, and cubic feet instantly.
Enter your slab's length, width, and thickness, and this calculator tells you exactly how much concrete you'll need. It converts your measurements into cubic feet, cubic yards, and the number of standard 80-lb bags—each bag yields about 0.6 cubic feet. For example, a 10 ft by 10 ft slab at 4 inches thick needs about 1.23 cubic yards, or 56 bags. That's the difference between ordering blind and pouring with confidence. Why does this matter? Concrete is sold by the cubic yard, but most people think in bags. Knowing both means you can order the right amount, avoid surplus, and keep the job moving. Read the results this way: cubic yards is what you'd order from a ready-mix company; bags is what you'd buy at the store; cubic feet is the raw volume. Use it before you plan your pour.
Pro tips
- Add 10% extra for waste, spillage, or uneven subgrade.
- Round your bag count up to the nearest full bag—never down.
- When ordering ready-mix, round up to the nearest quarter cubic yard.
- Double-check that all measurements are in the same units before you calculate.
Real-life examples
- Planning a backyard patio slab and need to know how many bags to haul.
- Ordering ready-mix for a new garage floor and need exact cubic yards.
- Estimating concrete for fence posts or footings without overbuying.
Case study
Before, Mark guessed at bag count for a 12x12 patio and ended up with 14 extra bags. After using this calculator, he entered his dimensions, saw he needed about 1.78 cubic yards, and ordered exactly the right number of bags—no waste, no rush trip.