How to use it
- Enter the length of your project in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Get your cubic yards, bags, and cubic feet instantly.
This calculator tells you exactly how much concrete you need — no guessing, no wasted money. Enter your slab's length, width, and thickness, and it instantly converts to cubic yards (the unit ready-mix trucks use), bags (for DIY projects), and cubic feet (for reference). For example, a 10 ft by 10 ft slab at 4 inches thick is 1.23 cubic yards — that's about 56 bags of 80-lb mix, since each bag yields 0.6 cubic feet. Why does this matter? Order too little and you're stuck mid-pour; too much and you've overpaid. Use the cubic yards figure when ordering from a concrete company, and the bag count when mixing on-site. Always round up to the nearest bag or fraction of a yard to stay safe. This tool works for patios, footings, sidewalks, or any slab — instantly, for free.
Pro tips
- Add 5-10% waste allowance to your final bag or yard count — spillage and uneven subgrades happen.
- Round bag quantities up to the nearest whole bag; you can't order a fraction of a bag.
- When ordering ready-mix, round up to the nearest quarter yard — trucks deliver in quarter-yard increments.
- Double-check thickness in inches, not feet — mixing units is the #1 cause of under-ordering.
Real-life examples
- Pouring a 10x12 patio slab and need to know how many bags to haul.
- Calculating ready-mix volume for a 20x30 garage foundation.
- Estimating concrete needed for a 2x4 form for a walkway.
Case study
Mark was pouring a 10x10 patio and guessed he needed 2 yards. He used this calculator, entered his numbers, and saw he only needed 1.23 yards — about 56 bags. He ordered 60 bags, saved nearly $200, and finished the job without a single extra trip.