What a 24x30 slab is for
A 24x30 slab is a two-car garage with a workshop bay, a deep garage for a boat or trailer, or a pole barn. At 720 square feet it is exactly at the limit of the floating garage slab in the Dubuque, Iowa, handout.
Concrete for a 24x30 slab at 4, 5 and 6 inches
Every inch of thickness on a 24x30 slab is 60 cubic feet, or 2.22 cubic yards. The ready mix order and the bags in this table include 10 percent extra. Change the thickness or the extra in the calculator above.
| Thickness | Cubic feet | Cubic yards | Ready mix to order | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 240 | 8.89 | 9.78 cu yd | 440 | 587 |
| 5 in | 300 | 11.11 | 12.22 cu yd | 550 | 734 |
| 6 in | 360 | 13.33 | 14.67 cu yd | 660 | 880 |
The 4 inch row by hand: 30 × 24 × 0.333 = 240 cubic feet, and 240 ÷ 27 = 8.89 cubic yards. With 10 percent extra that is 264 cubic feet. An 80 lb bag makes 0.60 cubic feet and a 60 lb bag makes 0.45, so it takes 440 of one or 587 of the other.
Quikrete says a sidewalk should be at least 4 inches thick and small slabs normally run 4 to 6 inches, depending on the load. The concrete slab calculator page covers what the building code asks for.
Bags or a truck for a 24x30 slab
From bags, it is 440 bags of 80 lb mix at 4 inches, 35,200 lb to lift and mix, about $2,504 at McCoy's price of $5.99 a bag, or $5.69 for 42 or more.
From a truck, it is 9.78 cubic yards, about $1,076 to $1,467 at HomeAdvisor's $110 to $150 per cubic yard delivered. The National Ready Mixed Concrete Association says a truck mixer carries 8 to 12 cubic yards, so this is about one truck load. Ask how much the supplier's trucks carry. If the order does not fill one, HomeAdvisor says a short-load fee of $40 to $60 per cubic yard can apply.
This is a truck job. 440 bags would be 35,200 lb to mix by hand, and they cost about $1,037 to $1,428 more than the ready mix. Check the route to the slab first. The association notes that a loaded truck weighs about 80,000 lb and may not be able to cross loose dirt or a residential curb.
| Thickness | 80 lb bags | Bags weigh | Bags cost | Ready mix | Ready mix cost |
|---|---|---|---|---|---|
| 4 in | 440 | 35,200 lb | $2,504 | 9.78 cu yd, about one truck load | $1,076 to $1,467 |
| 5 in | 550 | 44,000 lb | $3,130 | 12.22 cu yd, 2 truck loads | $1,344 to $1,833 |
| 6 in | 660 | 52,800 lb | $3,755 | 14.67 cu yd, 2 truck loads | $1,614 to $2,201 |
Prices are from the sources below, checked in October 2026; multiply the table by your own to compare. Gravel, steel, forms, finishing and labor are extra.
Pouring a 24x30 slab
At 4 inches, 9.78 cubic yards: one full truck. At 6 inches, 14.67 cubic yards, which takes two. When a pour needs two trucks, NRMCA says to tell the plant the rate you need them, so the second one arrives as the first runs out. A 24 foot width will not screed with one board, so set rails and pour in strips, with a crew of four or more.
Gravel base and slope
A 4 inch gravel base under a 24x30 slab is 240 cubic feet, or 8.89 cubic yards. Quikrete says to spread and compact 3 to 4 inches, and a 3 inch base is 180 cubic feet, or 6.67 cubic yards. Those are volumes of the finished layer. Gravel settles when it is compacted, so order a little more.
Outside, Quikrete says to slope the slab away from buildings and gives 1/4 inch per foot as the usual fall. Running across the 24 foot side, that is 6 inches from one edge to the other. Running along the 30 foot side, it is 7 1/2 inches. Set the forms to the slope, and the screed follows them.
As a garage floor
Dubuque, Iowa, publishes a simple foundation for a detached garage of up to 720 square feet: a floor at least 4 inches thick on a grade beam, a thickened edge at least 12 inches deep and 12 inches wide under every wall, with 6x6 welded wire or #4 bars no more than 2 feet apart both ways. A 24x30 garage is 720 square feet, exactly at that limit. Your town may want something else, especially where the ground freezes deep, so take this as an example and ask first.
The grade beam is the outer foot of the slab, made 8 inches deeper than the floor. Around a 24x30 slab that is 104 square feet of edge, 69.3 cubic feet, or 2.57 cubic yards more concrete. With 10 percent extra, that adds 2.82 cubic yards, for an order of about 12.6 at 4 inches. Dig the edge deeper if the grade falls away, because Dubuque measures the 12 inches from the ground outside.
Rebar or wire mesh
With bars 24 inches on center both ways, held 3 inches back from each edge, a 24x30 slab takes 13 bars 29 feet 6 inches long and 16 bars 23 feet 6 inches long. That is 760 feet of bar. With 10 percent extra, buy 42 bars 20 feet long. Every bar is longer than the 20 foot length sold, so each one is made of pieces that overlap. Fridley, Minnesota, says to overlap joined bars by at least 40 bar diameters, which is 20 inches for a 1/2 inch #4 bar. The 10 percent extra is there for those overlaps and the offcuts.
With wire mesh instead, 8 sheets 8 feet by 12.5 feet, lapped 8 inches, cover it. The spacing and the sheet size are where the calculator starts. Your plans or your building department set the steel for your slab.
Control joints
Quikrete says control joints in a 4 inch slab go every 6 to 8 feet and about a quarter of the slab deep, which is 1 inch. Keeping them no more than 8 feet apart cuts a 24x30 slab into 4 panels along the 30 foot side and 3 along the 24 foot side. That makes 12 panels, each 7 feet 6 inches by 8 feet, with 132 feet of joint to cut.
Before you pour a 24x30 slab
If the second truck is late, the edge of the first pour starts to set, and the joint between them can show or crack. Put a planned control joint where one truck's concrete ends, and keep the second truck booked on a firm time. The forms for a slab this long must be straight: check them with a string line before the truck arrives.
Other slab sizes
8x1010x1010x1212x1210x2012x2016x2020x2020x2424x2424x3030x40
Common questions
How much concrete do I need for a 24x30 slab?
A 24 by 30 foot slab 4 inches thick holds 240 cubic feet of concrete, which is 8.89 cubic yards. With 10 percent extra, order 9.78 cubic yards of ready mix. At 5 inches thick it holds 11.11 cubic yards and at 6 inches 13.33.
How many 80 lb bags of concrete do I need for a 24x30 slab?
440 bags at 4 inches thick, with 10 percent extra. They weigh 35,200 lb in all and cost about $2,504 at the store price checked in October 2026. At 5 inches thick it is 550 bags and at 6 inches 660.
How thick should a 24x30 concrete slab be?
Quikrete calls for at least 4 inches for a sidewalk and 4 to 6 inches for small slabs, depending on the load. The International Residential Code minimum for a house floor slab is 3.5 inches. On a 24x30 slab each extra inch adds 2.22 cubic yards, so going from 4 to 6 inches takes the ready mix order from 9.78 to 14.67 cubic yards. Ask your building department what it wants for a driveway or a garage floor.
How long do I have to finish a 24x30 slab?
Not long. NRMCA says concrete normally sets two to eight hours after mixing, and quickly on a hot day. Quikrete says troweling can start once the shine leaves the surface, 30 minutes to an hour on average. On 720 square feet, that means a crew of four or more, working in strips.
Can a 24x30 garage use a floating slab?
In some places. Dubuque, Iowa, allows a floating slab with a 12 inch deep, 12 inch wide thickened edge for detached garages up to 720 square feet, and 24x30 is exactly 720. Larger garages, and many towns in cold climates, need frost footings. Ask your building department.
How much concrete for a 24x30 garage slab with a thickened edge?
About 12.6 cubic yards with 10 percent extra: 9.78 for the 4 inch floor and 2.82 for a grade beam 12 inches deep and 12 inches wide around the edge, the kind Dubuque, Iowa, allows for a detached garage of up to 720 square feet.
Tools for this job
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- Form stakes. Hold the form boards in place while you pour.
- Concrete float. Smooths the surface after the concrete is leveled.
- Edger. Rounds the slab edges so they do not chip.
- Groover. Cuts control joints so cracks follow a straight line.
- Finishing trowel. Gives the slab its final smooth surface.
- Rubber boots. Keep wet concrete off your skin while you stand in the pour.
Sources
- Quikrete, Pouring and Finishing Concrete Slabs
- Quikrete, Concrete Sidewalks and Small Slabs project guide
- Quikrete Concrete Mix data sheet (yield per bag)
- National Ready Mixed Concrete Association, CIP 31: Ordering Ready Mixed Concrete
- International Residential Code 2021, Chapter 5: concrete floors on the ground (R506)
- International Residential Code 2021, Chapter 4: foundations (R403, concrete cover over steel)
- Wire Reinforcement Institute, Manual of Standard Practice: Structural Welded Wire Reinforcement
- City of Dubuque, Iowa, minimum requirements for a detached garage slab
- City of Fridley, Minnesota, Garage Slabs handout
- PJ's Rebar, stock rebar sizes and lengths
- International Residential Code 2021, Chapter 1: work exempt from permit (R105.2)
- McCoy's Building Supply: Quikrete Concrete Mix, 80 lb bag
- HomeAdvisor: concrete delivery cost, per cubic yard and short-load fees
Facts on this page were last checked against these sources in October 2026.