How Many Bags of Concrete Do I Need for a Slab?
For a small slab, bagged concrete mix is convenient. For a big pour, ready-mix delivery is cheaper and far less work. Here is how to figure out the bag count — and when to make the switch.
How bagged concrete is measured
Each bag yields a set volume of mixed concrete:
- 80 lb bag ≈ 0.60 cubic feet
- 60 lb bag ≈ 0.45 cubic feet
- 40 lb bag ≈ 0.30 cubic feet
Divide your slab's volume by the bag yield to get the number of bags.
Find your slab volume
Multiply the area (length × width in feet) by the thickness in feet. For example, a 10 ft × 10 ft slab at 4 inches (0.333 ft) thick is 100 × 0.333 = about 33 cubic feet. At 0.6 cubic feet per 80 lb bag, that's roughly 56 bags.
Open the concrete calculator → Enter your slab size and thickness to get the cubic yards and the exact number of 60 lb and 80 lb bags.
When to switch to ready-mix
Once you pass about one cubic yard (27 cubic feet, or roughly forty-five 80 lb bags), mixing bags by hand becomes slow and expensive. Ready-mix delivery is usually cheaper per yard at that point, though many suppliers have a minimum order (often one cubic yard) and a short-load fee below it.
Slab thickness and base
Use 4 inches for patios, walkways, and shed floors, and 5–6 inches for driveways or garage floors. Pour over a compacted gravel base and add wire mesh or rebar for strength and crack resistance.
Frequently asked questions
- How many 80 lb bags of concrete in a cubic yard?
- An 80 lb bag yields about 0.6 cubic feet, and a cubic yard is 27 cubic feet, so it takes about 45 bags to make one cubic yard.
- How many bags for a 10x10 slab?
- A 10 ft × 10 ft slab at 4 inches thick is about 33 cubic feet — roughly 56 bags of 80 lb mix or 74 bags of 60 lb mix. At that size, ready-mix is usually cheaper.
- How thick should a concrete slab be?
- 4 inches is standard for patios, walkways, and shed floors; 5–6 inches for driveways or anything carrying vehicle weight.
Last updated June 2026.