Concrete Bag Calculator
This concrete bag calculator figures out how many bags of concrete mix you need for a slab, footing, or post hole. Enter your length, width, and depth to get bag counts for 40, 50, 60, and 80 lb bags side by side.
- Volume
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- 40 lb bag
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- 50 lb bag
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- 60 lb bag
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- 80 lb bag
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| Bag size | Yield (ft³) | Bags per cubic yard |
|---|---|---|
| 40 lb bag | 0.3 | 90 |
| 50 lb bag | 0.375 | 72 |
| 60 lb bag | 0.45 | 60 |
| 80 lb bag | 0.6 | 45 |
| Use | Typical depth |
|---|---|
| Fence post footing | 6-12 in (post hole, not slab) |
| Walkway / patio slab | 4 in |
| Shed / garage floor | 4-6 in |
| Driveway slab | 5-6 in |
Frequently Asked Questions
How many 80 lb bags of concrete are in a yard?
An 80 lb bag of concrete yields about 0.6 cubic feet, so a cubic yard (27 cubic feet) needs 27 / 0.6 = 45 bags. That is the standard reference number most contractors use for 80 lb bags.
How many 60 lb bags of concrete are in a yard?
A 60 lb bag yields about 0.45 cubic feet, so a full cubic yard needs 27 / 0.45 = 60 bags. Smaller 40 lb bags yield about 0.3 cubic feet and need 90 bags per cubic yard.
How much concrete do I need for a 10x10 slab?
A 10x10 ft slab at a standard 4-inch depth needs about 1.23 cubic yards of concrete. In bagged form, that is roughly 56 bags of 80 lb mix or 75 bags of 60 lb mix.
How thick should a concrete slab be?
Most patio and walkway slabs are poured 4 inches thick, while driveways and garage floors typically use 5-6 inches to handle vehicle weight. Fence post footings are measured by hole depth rather than slab thickness, usually 6-12 inches below the frost line.
Is it cheaper to buy bagged concrete or ready-mix?
For small pours under about 1 cubic yard, bagged concrete mix is usually more practical and not much pricier than ordering ready-mix delivery. Larger pours are almost always cheaper per cubic yard with a ready-mix truck, which also saves the labor of mixing dozens of bags by hand.