12x24 Concrete Slab: Cost, Yards & Bags of Concrete
Quick answer: a 12 × 24 ft slab (288 sq ft) 4 inches thick needs 3.56 yd³ of concrete, 3.91 yd³ with 10% waste (order 4 yd³ of ready-mix) or 176 bags of 80-lb mix. Installed, it costs about $2,090 – $3,730 ($7.00 – $13.00 per sq ft); DIY materials run $870 – $1,330.
A 12 × 24 ft slab (288 sq ft) fits a single carport or a one-car parking pad with room to walk around the vehicle, or a long storage building. Carport kits in this size set their posts on the slab edge or on separate footings, so plan the slab and the posts together.
Concrete for a 12x24 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 (typical) | 3.56 yd³ | 3.91 yd³ | 4 yd³ | 176 | 235 | 352 | $2,090–$3,730 |
| 5 in | 4.44 yd³ | 4.89 yd³ | 5 yd³ | 220 | 294 | 440 | $2,240–$3,910 |
| 6 in | 5.33 yd³ | 5.87 yd³ | 6 yd³ | 264 | 352 | 528 | $2,380–$4,090 |
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 (4 in slab) | Concrete | 80-lb bags |
|---|---|---|
| 0% (exact volume) | 3.56 yd³ | 160 |
| 5% | 3.73 yd³ | 168 |
| 10% | 3.91 yd³ | 176 |
| 15% | 4.09 yd³ | 184 |
Bags or a Ready-Mix Truck?
| Option | What you buy | Concrete bill |
|---|---|---|
| 80-lb bags | 176 bags at $6.50 + mixer rental $75 | $1,219 |
| Ready-mix | 4 yd³ at $150 + $120 delivery + $140 short-load fee | $860 |
Ready-mix, without question. 176 bags would cost $1,219 and take about 7 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. Try your own prices in the bags vs. ready-mix calculator.
What a 12x24 Slab Costs
| Line item (4 in slab) | Basis | Cost |
|---|---|---|
| Ready-mix concrete + delivery | 3.91 yd³ at $150 + $120 | $707 |
| Forms | 72 lin ft at $2.20 | $158 |
| Vapor barrier | 288 sq ft at $0.35 | $101 |
| #4 rebar at 18 in | 288 sq ft at $1.25 | $360 |
| Broom finish | 288 sq ft at $0.75 | $216 |
| Labor (place & finish) | 288 sq ft at $5.00 | $1,440 |
| Direct cost | Before overhead and profit | $2,982 |
- Installed price: $2,090 – $3,730. 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 $400 – $950 more.
- 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 12 × 24 ft Slab
| Concrete | 4 yd³ ready-mix, or 176 × 80-lb / 352 × 40-lb bags |
|---|---|
| Gravel base (4 in compacted) | 4.09 yd³, about 5.7 tons |
| Forms | 6 × 2x4 boards 12 ft long, 26 stakes, 52 screws (72 lin ft) |
| Rebar (#4 at 18 in) | 409 lin ft = 21 × 20-ft sticks, 45 chairs |
| Or wire mesh (6x6) | 9 sheets of 5 × 10 ft, about $108 – $180 |
| Vapor barrier | 288 sq ft plus 6 in laps |
| Control joints | 6 panels of about 8 × 6 ft: 48 lin ft of saw cut, 1 in deep |
Recommended Specs for a Carport Or Parking Pad
| Thickness | 4 in for cars; 5 in for pickups, trailers and RVs |
|---|---|
| Strength | 3,500 PSI air-entrained; 4,000 PSI where de-icing salt is tracked in |
| Base | 4 to 6 in of compacted crushed stone |
| Reinforcement | #4 rebar at 18 in on chairs |
| Posts | Carport posts on their own footings (or thickened slab under each post), sized by the carport kit or engineer |
- Check where the carport kit wants its posts: many need a 12 × 12 in footing or a thickened slab under each post, not a 4-in slab edge.
- Pour 5 in thick if a pickup, trailer or RV will park on it.
- At 3.91 yd³ this is a ready-mix job; 176 bags would be several hours of mixing.
Pour Day for a 12x24 Slab
- Crew time: about 10 crew-hours to set forms, place, finish and cut joints (0.035 h per sq ft for a broom finish).
- Trucks: 4 yd³ is 1 truck, about 20–32 minutes of unloading in total. Concrete must be placed within 90 minutes of batching.
- Reach: a truck chute reaches about 15–20 ft, enough for this slab if the truck can park beside it. If it can't, budget wheelbarrows or a line pump.
- 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 12x24 Slab
The calculator below starts at 12 × 24 ft, 4 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.
12x24 Slab Questions
About $2,090 to $3,730 installed for a 4-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 $870 to $1,330. Site prep and a gravel base add about $400 to $950.
At 4 inches thick with 10% waste: 176 bags of 80-lb mix, 235 bags of 60-lb mix or 352 bags of 40-lb mix. At 6 inches: 264 bags of 80-lb mix.
At 4 inches, 3.56 cubic yards (order 4.00 with waste); at 5 inches, 4.44 (order 5.00); at 6 inches, 5.33 (order 6.00). Ready-mix is sold in quarter yards, so round up.
Ready-mix. 4 yards delivered costs about $860, while 176 bags would cost about $1,219 and take roughly 7 hours of mixing. Bags only win below about 1.3 cubic yards.
A #4 grid at 18 inches each way needs about 409 linear feet of bar including laps: 21 twenty-foot sticks and about 45 chairs. Welded wire mesh instead takes 9 sheets of 5 x 10 ft.
4 inches with #4 rebar is fine for cars; use 5 inches for pickups and trailers. The posts usually need their own footings or a thickened section, as the carport kit specifies.