How Much Concrete for a 24x24 Garage Slab? (Yards, Bags, and Cost)

A 24-foot by 24-foot garage is one of the most common slab sizes in North America, so it is worth knowing the exact concrete it takes before you call a supplier. The short answer: at 4 inches thick you need about 7.1 cubic yards of concrete, or roughly 7.9 cubic yards once you add the standard 10% waste allowance.

Here is how that breaks down — and how the number changes if you pour thicker, which most garage slabs should.

The cubic-yard math

Concrete volume is length times width times thickness, with everything in the same units, divided by 27 to convert cubic feet to cubic yards.

For a 24 × 24 slab at 4 inches (which is 0.333 feet):

• 24 × 24 = 576 square feet
• 576 × 0.333 = 192 cubic feet
• 192 ÷ 27 = 7.1 cubic yards
• 7.1 × 1.10 (waste) = about 7.9 cubic yards to order

At 5 inches thick — a better choice for a garage that parks trucks or heavy vehicles — the same slab needs about 8.9 cubic yards before waste, or roughly 9.8 with the allowance.

What it costs in 2026

At a typical 4,000 PSI ready-mix price of about $150 per cubic yard, the concrete alone for a 4-inch slab runs roughly $1,185 to $1,300 delivered. Step up to 5 inches and material climbs to around $1,470 to $1,600.

That is just the concrete. Installed — including base prep, forms, reinforcement, placing, and finishing — a garage slab typically runs $7 to $15 per square foot, which puts a finished 576-square-foot slab somewhere around $4,000 to $8,600 depending on thickness, reinforcement, and your local labor market.

Should you use bags instead?

No. Nearly 8 cubic yards is far past the point where bagged concrete makes sense. One 80 lb bag yields about 0.60 cubic feet, so a single cubic yard takes around 45 bags — and a 24 × 24 slab would need roughly 355 bags. Mixing that by hand is not realistic, and the risk of cold joints between batches is high. This is a ready-mix job.

Don't forget reinforcement and base

A garage slab carries rolling vehicle loads, so budget for a compacted gravel base, rebar or heavy wire mesh, a vapor barrier, and often thickened edges where walls and tires bear. Use 4,000 PSI concrete rather than 3,000 — the strength upgrade is cheap insurance against scaling and cracking.

Get your exact number

These figures assume a clean 24 × 24 rectangle. If your slab is a different size or you want to compare thicknesses, run it through the slab calculator — it converts your dimensions to cubic yards and a material cost range with the waste allowance already applied. Always confirm volume and price with your supplier before ordering.