Concrete Calculator
Find out how many cubic yards or bags of concrete you need for a slab, footing or round column.
| Option | Amount |
|---|---|
| 80 lb bags | 0 |
| 60 lb bags | 0 |
| 40 lb bags | 0 |
| Ready-mix truck | 0 |
| Estimated cost |
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How the concrete calculator works
Concrete is sold by volume. The calculator multiplies your dimensions to get cubic feet, divides by 27 to get cubic yards, then adds your waste percentage so you do not run short mid-pour.
- Slab: length x width x thickness (thickness converted from inches to feet).
- Footing: length x width x depth (width and depth converted from inches to feet).
- Round column or post hole: pi x radius squared x height, times the number of columns.
Worked example: a 10 ft x 10 ft patio, 4 inches thick
10 x 10 x (4 / 12) = 33.3 cubic feet, or 1.23 cubic yards. Add 10% for waste and you need about 1.36 cubic yards. In bagged mix that is roughly 62 bags of 80 lb concrete. A ready-mix truck order would be 1.5 cubic yards.
Bag yields used
| Bag size | Approx. yield |
|---|---|
| 40 lb | 0.30 cu ft |
| 60 lb | 0.45 cu ft |
| 80 lb | 0.60 cu ft |
Yields vary slightly by brand. Check the bag, and round up.
Frequently asked questions
How many 80 lb bags make a cubic yard?
About 45. An 80 lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet.
How much extra concrete should I order?
Five to ten percent is typical. Use 10% or more on rough or uneven ground, since a short pour is far worse than a little left over.
How thick should a concrete slab be?
Four inches is common for patios and walkways. Driveways and heavier loads often use 5 to 6 inches. Check local code and ask a contractor for load-bearing work.
Is bagged concrete or a truck cheaper?
For small jobs, bags. Once you are past roughly one cubic yard, delivered ready-mix is usually easier and often competitive, but short-load fees can apply on small orders.
Estimates only. Always confirm quantities and structural requirements with your supplier or a qualified contractor.