How Much Concrete for a 24x24 Garage Slab?

How much concrete for a 24x24 garage slab starts at about 7.11 cubic yards for a 4-inch floor and rises to about 8.89 cubic yards at 5 inches and 10.67 at 6 inches. That is just the flat floor. Many detached garages are poured with a thickened perimeter or sit on separate footings, and those can add 2 to 4 more yards. Here is how to add it all up before you call the ready-mix plant.

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Floor volume by thickness

A 24 by 24 foot garage has 576 square feet of floor.

Floor thickness	Cubic feet	Cubic yards
4 inches	192	7.11
5 inches	240	8.89
6 inches	288	10.67

Adding a thickened edge

A monolithic slab, sometimes called a floating slab, thickens around the outside so the walls bear on deeper concrete. The size of that edge is set by local code and the plans, but a common example is 12 inches wide and 12 inches deep in total, which is 8 inches below a 4-inch floor.

The perimeter of a 24x24 garage is 96 feet. An edge that is 1 foot wide and 0.667 feet deeper than the floor adds 96 × 1 × 0.667 = 64 cubic feet, or about 2.37 cubic yards. Wider or deeper edges add more; an 18-inch-wide by 12-inch-deeper edge would add about 5.3 yards. Measure your actual trench before ordering, since excavators rarely dig to the exact line.

In colder regions, a detached garage often needs frost-depth footings and a stem wall instead of a floating slab. In that case, the footings and walls are usually poured first, and the floor is a separate, smaller pour.

Putting the order together

For a 4-inch floor with the 12-by-12 thickened edge in the example:

Floor: 7.11 cubic yards.
Edge: about 2.37 cubic yards.
Subtotal: about 9.5 cubic yards.
Add 5 to 8 percent for waste and base variation: about 10 to 10.25 yards.

Many ready-mix trucks carry 8 to 10 yards, so this pour may take two trucks. Ask the dispatcher to time the second truck so it arrives as the first finishes, and confirm the plant’s per-truck minimums.

Floor thickness for a garage

4 inches is a widely used minimum for a garage holding passenger cars on a good base.
5 inches is a popular upgrade for extra stiffness at a modest cost.
6 inches suits pickups with heavy loads, car lifts, or a shop floor. A car lift may need a thicker pad at the posts; follow the lift maker’s requirements.

Slope, the door landing, and joints

Garage floors usually slope gently toward the overhead door so meltwater and wash water run out. A slope of about 1/8 inch per foot is a common target. The transition at the door matters too; see the level landing at the garage door for how the apron and floor meet.

For joints, a 24x24 floor at 4 to 5 inches thick is often split into four 12x12 panels. Some builders add more joints or reinforcement to keep panels closer to 10 feet.

Base material

A 4-inch compacted crushed stone base under 576 square feet is about 7.1 cubic yards, or roughly 10 to 10.7 tons. Sand or stone fill inside the thickened edge, when the grade needs to come up, adds more. Many garage floors also get a vapor barrier over the base to slow moisture from the ground.

Questions people ask

How many yards of concrete for a 24x24 garage floor?

About 7.11 cubic yards for a 4-inch floor, 8.89 for 5 inches, and 10.67 for 6 inches, before thickened edges or waste.

How much extra concrete does a thickened edge add?

For a 24x24 slab with an edge 12 inches wide that drops 8 inches below a 4-inch floor, about 2.4 cubic yards. Larger edges add more.

Will a 24x24 slab take more than one truck?

Often, yes. With a thickened edge, the order can reach 9 to 11 yards, more than many trucks carry in one load.

How thick should a 24x24 garage slab be?

Four inches is a common minimum for cars, 5 inches adds margin, and 6 inches suits heavy trucks, lifts, or shop use. Local code may set more.

How much gravel goes under a 24x24 garage slab?

About 7.1 cubic yards for a 4-inch compacted base, roughly 10 to 10.7 tons, plus any fill needed to raise the grade.

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