How to use it
- Enter the slab length in feet.
- Enter the slab width in feet.
- Enter the slab thickness in inches.
- Press calculate for cubic yards, cubic feet, and bag count.
This slab calculator turns your slab dimensions into the exact concrete volume you need. Enter length, width, and thickness, and you get cubic yards, cubic feet, and the number of 80-lb bags. The math uses the standard yield of 0.6 cubic feet per 80-lb bag, so your bag count is based on real-world coverage.
Knowing your cubic yards matters if you're ordering ready-mix concrete—trucks are measured by the yard. Cubic feet help you compare bag sizes, and the bag count tells you how many trips to the store you'll avoid. For example, a 10 ft x 10 ft x 4 in slab is about 33.3 cubic feet, 1.23 cubic yards, and 56 bags (rounding up). That's the difference between a finished patio and a half-poured one.
Read the results like this: use cubic yards for delivery, cubic feet for volume, and bags for your shopping list. Always round up when buying bags.
Pro tips
- Add 5-10% for waste—broken bags, spills, or uneven subgrades.
- Always round bag counts up to the next whole bag; you can't buy a fraction of a bag.
- For large slabs, compare bag price vs. ready-mix delivery; over 1 cubic yard, ready-mix may be cheaper.
- Don't mix units—convert thickness to feet before calculating, or the result will be wrong.
Real-life examples
- Pouring a backyard patio and need to know exactly how many bags to haul.
- Planning a shed foundation slab and comparing ready-mix vs. bag delivery.
- Quoting a concrete walkway job and need cubic yards for a customer estimate.
Case study
Before using the calculator, Dana guessed she needed 80 bags for her 10x10 patio. After entering her dimensions, she saw the real number was 56 bags—plus 10% waste made it 62. She ordered exactly that, finished in a day, and returned nothing.