How to use it
- Enter the slab length in feet.
- Enter the slab width in feet.
- Enter the thickness in inches.
- Hit Calculate to see cubic yards, bags, and cubic feet.
This calculator takes the length and width of your slab in feet and the thickness in inches, then instantly returns the concrete volume in cubic yards, cubic feet, and the number of standard 80-lb bags needed. It uses the standard yield of 0.6 cubic feet per 80-lb bag, so you get a realistic bag count without guesswork. The cubic yards figure matters most when ordering ready-mix concrete; the bag count matters for smaller DIY jobs where you'll mix by hand. To read the results, look at cubic yards for your ready-mix order, then check bags to see how many 80-lb sacks that equals—or use cubic feet if you're comparing with other materials. This tool helps you buy the right amount, avoid expensive overage, and prevent a shortfall that stalls your project.
Pro tips
- Add 10% waste to the final bag count.
- Round up to the nearest whole bag—partial bags aren't sold.
- For slabs larger than a yard, consider ordering ready-mix instead of bags.
- Double-check the thickness in inches—a 1-inch error changes volume by 25%.
Real-life examples
- Pouring a backyard patio slab.
- Setting fence posts with concrete footings.
- Laying a sidewalk path.
Case study
Before, Dave ordered 80 bags for a 10x10x4 slab and had 24 left over. After using this calculator, he saw he needed only 56 bags and saved $120.