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Concrete Calculator: Cubic Yards to Bags
Enter the length, width, and depth of your pour. This tool converts your dimensions straight to cubic yards, cubic feet, and the number of bags you'll need to buy.
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How the math works
Concrete is sold by volume, so the calculation is straightforward once you have three measurements: length, width, and depth. The formula:
cubic yards = cubic feet ÷ 27
bags needed = cubic feet ÷ yield per bag
Depth is usually measured in inches, so divide it by 12 first to convert to feet before multiplying. A cubic yard is 27 cubic feet (3 × 3 × 3), which is why that division shows up in the second step.
Bag yield reference
| Bag size | Yield | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | ~90 bags |
| 60 lb | 0.45 cu ft | ~60 bags |
| 80 lb | 0.60 cu ft | ~45 bags |
Common mistakes
The two things that throw off a concrete estimate most: forgetting to convert depth from inches to feet before multiplying, and not accounting for waste. Uneven sub-grade, form leakage, and general spillage routinely eat 5–10% more material than the raw math suggests — round up rather than cutting it exact, especially if a return trip to the store means a delay in your pour.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45 bags of 80 lb concrete mix make one cubic yard, since each 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet.
How thick should a concrete slab be?
A standard walkway or patio slab is typically 4 inches thick. Driveways for vehicles are usually poured at 5 to 6 inches to handle the extra load.
Should I round up when buying concrete bags?
Yes. Uneven ground, spillage, and measurement rounding typically use up 5 to 10 percent more material than the raw calculation, so buying a bag or two extra avoids a second trip.
Planning a patio specifically?
See our full concrete patio cost guide for a materials-vs-labor breakdown, finish-type pricing, and where DIY actually saves money.