How to use it
- Enter the length of your slab or area in feet.
- Enter the width in feet.
- Enter the thickness in inches.
- Click Calculate to see cubic yards, bags, and cubic feet.
This concrete calculator turns your length, width, and thickness into the exact material quantities you need — cubic yards for ordering ready-mix, cubic feet for comparing bulk deliveries, and the number of standard 80-lb bags for DIY projects. Each 80-lb bag yields about 0.6 cubic feet, so the bag count is automatically adjusted to match your volume. The result tells you exactly how much concrete to buy, preventing both shortfalls and costly leftovers. You'll see three numbers: total cubic feet (the raw volume), cubic yards (the unit ready-mix companies use), and bags (the practical count for bagged mix). Use the cubic yard number if you're ordering a truck, or the bag count if you're hauling bags yourself. This removes guesswork from patios, footings, and slabs — so you order once, mix once, and finish the job without running out.
Pro tips
- Add 10% extra to your final bag count to cover spillage, uneven subgrade, or slight form deflection.
- Round bag counts up to the next whole bag — you can't buy a fraction of a bag, and mixing a partial batch is impractical.
- When ordering ready-mix, round up to the nearest quarter yard; most suppliers won't deliver less than a full yard.
- Double-check your thickness in inches — a common mistake is mixing feet and inches, which throws off the volume by 12x.
Real-life examples
- Pouring a 10x10 ft patio slab at 4 inches thick to know how many bags to load.
- Planning a 2x2 ft concrete footing for a deck post and ordering the exact bag count.
- Estimating ready-mix for a 20x30 ft driveway before calling the supplier.
Case study
Dan needed a 12x15 ft slab, 6 inches thick. He guessed 60 bags, but the calculator showed 75 bags — a 25% difference. He bought the right amount, finished in one day, and didn't make a second trip.