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, cubic feet, and 80-lb bag count.
This free concrete calculator tells you exactly how much concrete you need for any slab, footing, or walkway. Enter the length and width in feet plus thickness in inches, and you instantly get the volume in cubic feet and cubic yards — plus the number of standard 80-lb bags required. Why does this matter? Ordering too little means a cold joint and a weak patch; ordering too much means wasted money and a messy cleanup. The calculator uses the standard yield of 0.6 cubic feet per 80-lb bag, so your bag count is always realistic. Read the results this way: cubic yards is what ready-mix companies quote; cubic feet helps you compare bag sizes; bags tells you how many to carry home. Whether you're pouring a small pad or a big slab, this tool removes guesswork and helps you budget accurately. It's fast, free, and built for real-world projects.
Pro tips
- Add 10% waste for spillage, uneven subgrade, or slight depth variations — concrete never comes out perfectly level.
- Round your bag count up to the nearest whole bag. Partial bags are useless, and you can always return unopened extras.
- If you're ordering ready-mix, round up to the nearest quarter yard. Most suppliers won't deliver less than that, and shortfalls are costly.
- Don't mix units — measure thickness in inches and length/width in feet. Converting wrong is the #1 cause of under-ordering.
Real-life examples
- Pouring a 10x12 ft patio slab at 4 inches thick.
- Setting fence posts with a 2-ft-deep, 8-inch-diameter hole.
- Building a 3x5 ft concrete stair landing or step pad.
Case study
Mark planned a 20x30 ft garage slab but kept guessing bag counts. He used this calculator, entered 20 by 30 by 4 inches, and saw he needed 12.5 cubic yards — 556 bags. He ordered ready-mix instead, saved $300 by not overordering, and finished the pour in one day.