How to use it
- Enter the slab length in feet.
- Enter the slab width in feet.
- Enter the thickness in inches.
- Click Calculate to see cubic yards, bags, and cubic feet.
This concrete calculator tells you exactly how much material you need for any rectangular slab. Enter length, width, and thickness, and it instantly returns cubic yards, cubic feet, and the number of standard 80-lb bags required.
Why does this matter? Ordering too little concrete means a cold joint and a weak slab. Ordering too much wastes money and leaves you hauling away extra. The calculator uses the standard conversion that 1 cubic yard equals 27 cubic feet, and each 80-lb bag yields 0.6 cubic feet. That means you can confidently order bags for small jobs or compare with ready-mix for larger pours.
Read the results this way: cubic yards is what ready-mix companies quote, bags is what you'll buy at the store, and cubic feet helps you visualize the volume. Use the tips below to avoid waste and finish your project right the first time.
Pro tips
- Add 5–10% waste to your total, especially for uneven ground or spillage.
- Round up to the nearest whole bag — partial bags aren't sold.
- Order extra bags for small jobs; you can always return unopened ones.
- Double-check thickness in inches, not feet — mixing units is the #1 mistake.
Real-life examples
- Pouring a concrete patio slab for your backyard.
- Setting fence posts or footing forms.
- Laying a sidewalk or walkway path.
Case study
Jake ordered 2 yards for his patio last month and ran short. This time he measured, entered length, width, and thickness into the calculator, got 1.8 yards, added 10% waste, and ordered 2 yards. He finished the pour in one trip — no extra hauling, no cold joint.