Estimate cubic yards, bag counts, and cost for a concrete pour, and subtract any voids like columns or sleeves from the total.
How This Is Calculated
Volume is length times width times thickness, converted to cubic feet and then cubic yards. Any voids you enter get subtracted from that total before it's converted to bag counts, so you're not ordering concrete for space that won't get poured.
Worked Example
Say you're pouring a 12 ft x 10 ft patio slab at 4 inches thick. Enter those dimensions and you'll get 1.48 cubic yards. At $150 a yard for ready-mix, that's $222.22 delivered, or about 67 bags of 80 lb pre-mix if you're hand-mixing it yourself.
Common Mistakes
- Forgetting to subtract voids (support columns, drain sleeves) before ordering, leading to over-ordering.
- Not checking your ready-mix supplier's minimum order size before assuming a small pour qualifies for truck delivery.
- Not padding for waste. This calculator gives the exact math, not a safety margin for spillage or an uneven subgrade.
Frequently Asked Questions
- How many 80 lb bags of concrete do I need per cubic yard?
- About 45 bags, though this calculator does that math for your exact slab automatically.
- Should I order concrete by the yard or by the bag?
- For anything over roughly 1-2 cubic yards, ready-mix by the truck is almost always cheaper and faster than bagged concrete.
- Do I need to add extra for waste when ordering concrete?
- Most contractors pad 5-10% for spillage and subgrade unevenness. This tool gives the exact volume, not a safety margin.