How much concrete for a 24x24 garage slab?
7.1 cu yd of concrete for a 24x24 garage slab, at the settings most people start with. Below the calculator are the same numbers for the alternatives you are likely to choose, and what each one does to the total.
Reviewed · Method: measured dimensions, industry coverage rates, rounded up to real package sizes · How the numbers are calculated
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The answer, and what it is made of
A 24 x 24 ft slab at 4 in thick is 7.1 cu yd of concrete. That is 337 bags at 80 lb each, which is why this size usually goes ready-mix: 337 bags is a long day with a mixer, and the truck arrives at a consistent slump instead of however you happened to mix the fortieth bag.
Planning figure for everything on that list: $2,509 to $3,809, with $3,055 as the realistic middle for the products most people actually buy. These are estimates for budgeting, not quotes. Prices move by region and by season, and the middle figure assumes a mid-range product rather than the cheapest thing on the shelf.
Thickness is the expensive variable: 7.1 cu yd at 4 in becomes 10.7 cu yd at 6 in, a jump of 51%. That extra concrete does less for crack resistance than a properly compacted base, which costs a fraction as much.
What changes if you change one thing
| Change the slab thickness | You buy |
|---|---|
| 4 in slab, cars only | 7.1 cu yd |
| 5 in slab, truck or lift | 8.9 cu yd |
| 6 in slab, two-post lift | 10.7 cu yd |
Every row is a live calculation, not an estimate. The shaded row is what this page defaults to.
What goes in the cart
| Item | Quantity |
|---|---|
| Concrete mix, 80 lb | 337 bags |
| Concrete mix, 60 lb (alternative) | 449 bags |
| Crushed gravel base | 10 tons (192 cu ft) |
| 6 mil vapor barrier | 576 sq ft |
| Form boards + stakes | 96 ft |
| Control joints | 3 runs |
Above 1 cubic yard, call the truck. 337 bags is 26,960 lb to haul and mix before it sets. A short-load fee beats a failed pour.
What this size actually changes
Seven cubic yards is a full truck and then some: a standard ready-mix truck carries 8 to 10 yards, so this arrives as one load with a little margin. It also means the pour is a morning's work with three or four people, a screed, a bull float and a power trowel — the point where a garage slab stops being a DIY job and becomes a crew job.
Figure. 24x24 garage slab at 4 in thick over a compacted base. Thickness sets the volume; the base sets whether it cracks.
How the quantity is worked out
Concrete is ordered by the cubic yard and sold in bags by weight, and the gap between those two units is where most estimates go wrong. A yard is 27 cubic feet, so a 10x12 slab at 4 in thick is 40 cu ft, or 1.5 cu yd. Rounded to whole yards at the ready-mix plant, that is 1.5 or 2 — and the shortfall shows up as a slab that is an inch thin at one corner.
Thickness is the expensive variable. Going from 4 in to 5 in on the same footprint adds 25 percent to the volume and 25 percent to the bill. Depth of the compacted base is the cheap variable: a proper 4 to 6 in base costs far less than an extra inch of concrete and prevents most of the cracking that a thicker slab would not have fixed anyway.
How to measure this job
Measure the inside of the garage walls, not the outside of the building. A 24x24 ft garage is 24 ft clear inside, which is 576 sq ft, and the slab may extend past the overhead door by a foot or so. If there is an apron outside the door, measure it as a separate rectangle — it is often a different thickness from the main slab.
Thickness should be specified before you price anything. A 4 in slab for cars, 5 in if a truck or a lift is going in, and 6 in with rebar for a two-post lift. The difference between 4 and 6 in on 576 sq ft is 3.6 cubic yards, which is real money.
Mistakes that cost real money
Ordering exactly the calculated volume
Ready-mix is delivered in whole yards and you cannot add half a yard on site. Order 5 to 10 percent over, because spillage, an uneven subgrade and a slightly deeper edge all consume concrete. Running short mid-pour produces a cold joint, which is a permanent weak line.
Pouring 4 in where a lift will go
A two-post lift puts point loads through the slab that a 4 in unreinforced slab cannot take. The footing requirements come from the lift manufacturer and are specific: thickness, concrete strength and rebar. Get the specification before the pour, not after.
Ordering exactly seven yards with no allowance
On 576 sq ft, a 1 in variation in subgrade depth is 1.8 cubic yards. Order 7.4 to 7.7 yards. The plant will charge for the extra rather than let you run short, and running short on a garage slab means a cold joint down the middle of the floor.
Forgetting the apron and the door threshold
The apron outside the overhead door is usually a separate, smaller pour and a different thickness. If it is part of the same slab, the door threshold detail changes. Measure and price it separately, because it never appears in a garage floor area calculation.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
Forty-five. An 80 lb bag yields about 0.6 cu ft, and a cubic yard is 27 cu ft. That means a 1.5 cu yd slab needs roughly 68 bags, which is why anything past about one yard usually goes ready-mix: 68 bags is a long day with a mixer and a lot of lifting.
How much concrete for a 24x24 garage slab?
At 4 in thick, 7.1 cubic yards; at 5 in, 8.9; at 6 in, 10.7. Order 5 to 10 percent over, and expect a ready-mix truck rather than bags — 7 yards is over 300 bags.
How much concrete for a 24x24 garage slab?
7.1 cubic yards at 4 in, 8.9 at 5 in, 10.7 at 6 in. Order 5 to 10 percent over. At this volume the truck comes to you, and the short-load and waiting charges are worth asking about before the day.
How many control joints in a 24x24 slab?
At 4 in thick, joints at 8 to 12 ft, so a grid roughly every 8 to 10 ft. On 24 ft that is two interior joint lines each way. Saw-cut within 24 hours, or tool them during finishing, then fill them with a flexible sealant.
What will the materials for this cost?
A planning range of $2,509 to $3,809 for everything in the shopping list, with $3,055 as the realistic middle. That is materials only: it excludes labour, delivery, tool hire and disposal of the old surface. Treat it as a budgeting figure, not a quote.