How to use it
- Enter the slab or project length in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Click calculate to see cubic yards, total cubic feet, and 80-lb bag count.
This calculator tells you exactly how much concrete you need for any slab or footing. Enter your length, width, and thickness, and it instantly returns three numbers: cubic feet, cubic yards, and the number of standard 80-lb bags required.
Why it matters: ordering too little means a mid-pour trip to the store; ordering too much wastes money and leaves you with heavy bags to dispose of. The result is based on the standard yield that one 80-lb bag covers about 0.6 cubic feet, so every calculation stays realistic for job-site planning.
Read the results this way: cubic yards is what ready-mix companies quote, bags is what you'll buy at the store for smaller jobs, and cubic feet helps you compare volumes directly. If your numbers seem high, double-check that you entered thickness in inches, not feet. This tool works for slabs, footings, steps, or any shape you can break into a rectangle.
Pro tips
- Add 10% to your total as a waste allowance for spillage, uneven subgrades, or slight over-dig.
- Round up to the nearest whole bag – you can't buy a fraction of a bag, and it's better to have a little extra.
- When ordering ready-mix, round up to the nearest quarter cubic yard to avoid short-load fees.
- Don't mix units – always convert thickness to inches and length/width to feet before calculating.
Real-life examples
- Planning a 10x10 concrete slab for a backyard shed.
- Pouring a 24-foot walkway and need to know how many bags to buy.
- Estimating material cost for a concrete footings project before hiring a contractor.
Case study
Before, Dave guessed his 10x10 slab needed 40 bags. After using the calculator, he ordered 55, avoiding a mid-pour run to the store and saving leftover mix. The job finished in one afternoon, not three days.