24x30 Concrete Slab: Cost, Yards & Bags of Concrete
Quick answer: a 24 × 30 ft slab (720 sq ft) 5 inches thick needs 11.11 yd³ of concrete, 12.22 yd³ with 10% waste (order 12.25 yd³ of ready-mix) or 550 bags of 80-lb mix. Installed, it costs about $5,250 – $9,350 ($7.00 – $13.00 per sq ft); DIY materials run $2,190 – $3,340.
A 24 × 30 ft slab (720 sq ft) is a roomy two-car garage with space for a workbench, storage and a second fridge. Poured 5 in thick it needs 12.22 yd³ in 2 trucks, and a crew of three or four finishers working together before it sets.
Concrete for a 24x30 Slab at 4, 5 and 6 Inches
| Thickness | Net volume | With 10% waste | Ready-mix order | 80-lb bags | 60-lb bags | 40-lb bags | Installed |
|---|---|---|---|---|---|---|---|
| 4 in | 8.89 yd³ | 9.78 yd³ | 10 yd³ | 440 | 587 | 880 | $4,880–$8,900 |
| 5 in (typical) | 11.11 yd³ | 12.22 yd³ | 12.25 yd³ | 550 | 734 | 1,100 | $5,250–$9,350 |
| 6 in | 13.33 yd³ | 14.67 yd³ | 14.75 yd³ | 660 | 880 | 1,320 | $5,620–$9,810 |
How Much Extra to Order
The table above adds 10%, the usual allowance for a formed slab on a graded base. Pick less only for rigid forms on a laser-flat base, more for soft or uneven ground:
| Waste allowance (5 in slab) | Concrete | 80-lb bags |
|---|---|---|
| 0% (exact volume) | 11.11 yd³ | 500 |
| 5% | 11.67 yd³ | 525 |
| 10% | 12.22 yd³ | 550 |
| 15% | 12.78 yd³ | 575 |
Bags or a Ready-Mix Truck?
| Option | What you buy | Concrete bill |
|---|---|---|
| 80-lb bags | 550 bags at $6.50 + mixer rental $75 | $3,650 |
| Ready-mix | 12.25 yd³ at $150 + $120 delivery | $1,958 |
Ready-mix, without question. 550 bags would cost $3,650 and take about 22 hours of mixing, far longer than concrete stays workable, so the slab would end up with cold joints. Ready-mix trucks bring it as fast as the crew can place it (2 trucks of about 8–10 yd³ each). Try your own prices in the bags vs. ready-mix calculator.
What a 24x30 Slab Costs
| Line item (5 in slab) | Basis | Cost |
|---|---|---|
| Ready-mix concrete + delivery | 12.22 yd³ at $150 + $120 | $1,953 |
| Forms | 108 lin ft at $2.20 | $238 |
| Vapor barrier | 720 sq ft at $0.35 | $252 |
| #4 rebar at 18 in | 720 sq ft at $1.25 | $900 |
| Broom finish | 720 sq ft at $0.75 | $540 |
| Labor (place & finish) | 720 sq ft at $5.00 | $3,600 |
| Direct cost | Before overhead and profit | $7,483 |
- Installed price: $5,250 – $9,350. The low end is a plain slab with lower-cost labor; the high end is the full scope above plus 25% contractor overhead and profit.
- Site prep and gravel base (excavation and 4 in of compacted stone): about $1,010 – $2,380 more.
- Thickened edge (12 in wide, 12–18 in deep) if the building sits on the slab: 2.5–4.6 yd³ more concrete, about $370 – $690, plus trenching and two #4 bars around the edge.
- Permit, where one is needed: about $50 – $350.
Have a contractor's price? Put it into the concrete quote checker, or compare two or three bids side by side there.
Materials List for a 24 × 30 ft Slab
| Concrete | 12.25 yd³ ready-mix, or 550 × 80-lb / 1,100 × 40-lb bags |
|---|---|
| Gravel base (4 in compacted) | 10.22 yd³, about 14.3 tons |
| Forms | 10 × 2x6 boards 12 ft long, 42 stakes, 84 screws (108 lin ft) |
| Rebar (#4 at 18 in) | 1,036 lin ft = 52 × 20-ft sticks, 99 chairs |
| Or wire mesh (6x6) | 21 sheets of 5 × 10 ft, about $252 – $420 |
| Vapor barrier | 720 sq ft plus 6 in laps |
| Control joints | 6 panels of about 10 × 12 ft: 78 lin ft of saw cut, 1.25 in deep |
Recommended Specs for a Garage Floor
| Thickness | 4 in minimum, 5 in typical; 6 in for heavy trucks or a lift |
|---|---|
| Strength | 3,500 PSI air-entrained (IRC minimum for garage floors in severe weathering areas) |
| Base | 4 to 6 in of compacted crushed stone, plus a 10-mil vapor barrier under heated or finished garages |
| Reinforcement | #4 rebar at 18 in on chairs |
| Edge | Monolithic thickened edge (12 in wide, 12-18 in deep) or a stem wall on footings, per your permit |
- Use 3,500 PSI air-entrained concrete, or 4,000 PSI if salt-covered cars park inside.
- Ask for a vapor barrier if you may heat or finish the garage later.
- A thickened edge or stem wall is needed under the walls; the cost section shows the thickened-edge add-on.
Pour Day for a 24x30 Slab
- Crew time: about 25 crew-hours to set forms, place, finish and cut joints (0.035 h per sq ft for a broom finish).
- Trucks: 12.25 yd³ is 2 trucks, about 61–98 minutes of unloading in total. Concrete must be placed within 90 minutes of batching.
- Reach: a truck chute reaches about 15–20 ft. At 24 ft wide, the middle is out of reach from one side, so plan access on two sides, a buggy, or a pump ($600 – $1,200).
- Joints: saw-cut 4–12 hours after finishing with a wet saw, or 1–4 hours with an early-entry saw.
- Curing: foot traffic after 24–48 hours, cars after 7 days, full strength at 28 days.
Price Your Own 24x30 Slab
The calculator below starts at 24 × 30 ft, 5 inches. Change the thickness, finish or reinforcement, pick your state for local prices, and the Live Estimate updates with a blueprint of the joint and rebar layout.
Concrete Slab Cost & Volume Estimator
Precision multi-layer project budgeting: Materials, Sub-Base, Reinforcement, Labor & Equipment
Picking a location sets the ready-mix, excavation and labor rates below to that area's typical level. You can still type your own local prices afterwards. Slab prices by state.
Closer spacing uses more steel and raises the rebar cost.
Not charged when bagged concrete is selected.
A scaled plan of your slab: rebar grid at the spacing you chose, support chairs about every 3 to 4 ft, and the recommended control-joint saw cuts (2.5 times the thickness in inches, in feet, capped at 15 ft). It redraws as you change the inputs.
| Scope Item / Material Description | Amount |
|---|
Enter the total your contractor quoted. We compare it with a benchmark for the same slab and scope you set in the calculator: materials at your entered prices plus labor at the regional standard rate, before any overhead or profit. Make sure the calculator scope (base, rebar, finish, pump, demolition) matches what the bid includes.
Optional: enter the bid's line items to see where the markup sits
Enter the forecast for pour day. The check follows ACI 306R (cold weather) and ACI 305R (hot weather) and estimates the surface evaporation rate that drives plastic shrinkage cracking.
24x30 Slab Questions
About $5,250 to $9,350 installed for a 5-inch slab with forms, a broom finish and labor ($7.00 to $13.00 per sq ft), at U.S. average prices. DIY materials run about $2,190 to $3,340. Site prep and a gravel base add about $1,010 to $2,380.
At 4 inches thick with 10% waste: 440 bags of 80-lb mix, 587 bags of 60-lb mix or 880 bags of 40-lb mix. At 5 inches: 550 bags of 80-lb mix.
At 4 inches, 8.89 cubic yards (order 10.00 with waste); at 5 inches, 11.11 (order 12.25); at 6 inches, 13.33 (order 14.75). Ready-mix is sold in quarter yards, so round up.
Ready-mix. 12.25 yards delivered costs about $1,958, while 550 bags would cost about $3,650 and take roughly 22 hours of mixing. Bags only win below about 1.3 cubic yards.
A #4 grid at 18 inches each way needs about 1,036 linear feet of bar including laps: 52 twenty-foot sticks and about 99 chairs. Welded wire mesh instead takes 21 sheets of 5 x 10 ft.
The installed range on this page covers a 5-inch slab with forms, vapor barrier, #4 rebar and a broom finish. A monolithic thickened edge adds the amount shown in the cost section; excavation and gravel are extra.