24x36 Concrete Slab: Cost, Yards & Bags of Concrete
Quick answer: a 24 × 36 ft slab (864 sq ft) 5 inches thick needs 13.33 yd³ of concrete, 14.67 yd³ with 10% waste (order 14.75 yd³ of ready-mix) or 660 bags of 80-lb mix. Installed, it costs about $6,260 – $11,170 ($7.00 – $13.00 per sq ft); DIY materials run $2,580 – $3,970.
A 24 × 36 ft slab (864 sq ft) is a three-car garage, or a two-car garage with a deep shop bay. It is a big residential pour: 14.67 yd³ at 5 in, which the plant sends in 2 trucks, and a slab this wide is hard to reach from the chute on every side.
Concrete for a 24x36 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 | 10.67 yd³ | 11.73 yd³ | 11.75 yd³ | 528 | 704 | 1,056 | $5,820–$10,620 |
| 5 in (typical) | 13.33 yd³ | 14.67 yd³ | 14.75 yd³ | 660 | 880 | 1,320 | $6,260–$11,170 |
| 6 in | 16.00 yd³ | 17.60 yd³ | 17.75 yd³ | 792 | 1,056 | 1,584 | $6,700–$11,720 |
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) | 13.33 yd³ | 600 |
| 5% | 14.00 yd³ | 630 |
| 10% | 14.67 yd³ | 660 |
| 15% | 15.33 yd³ | 690 |
Bags or a Ready-Mix Truck?
| Option | What you buy | Concrete bill |
|---|---|---|
| 80-lb bags | 660 bags at $6.50 + mixer rental $75 | $4,365 |
| Ready-mix | 14.75 yd³ at $150 + $120 delivery | $2,333 |
Ready-mix, without question. 660 bags would cost $4,365 and take about 26 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 24x36 Slab Costs
| Line item (5 in slab) | Basis | Cost |
|---|---|---|
| Ready-mix concrete + delivery | 14.67 yd³ at $150 + $120 | $2,320 |
| Forms | 120 lin ft at $2.20 | $264 |
| Vapor barrier | 864 sq ft at $0.35 | $302 |
| #4 rebar at 18 in | 864 sq ft at $1.25 | $1,080 |
| Broom finish | 864 sq ft at $0.75 | $648 |
| Labor (place & finish) | 864 sq ft at $5.00 | $4,320 |
| Direct cost | Before overhead and profit | $8,934 |
- Installed price: $6,260 – $11,170. 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 $1,210 – $2,850 more.
- Thickened edge (12 in wide, 12–18 in deep) if the building sits on the slab: 2.8–5.1 yd³ more concrete, about $410 – $770, 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 × 36 ft Slab
| Concrete | 14.75 yd³ ready-mix, or 660 × 80-lb / 1,320 × 40-lb bags |
|---|---|
| Gravel base (4 in compacted) | 12.27 yd³, about 17.2 tons |
| Forms | 10 × 2x6 boards 12 ft long, 46 stakes, 92 screws (120 lin ft) |
| Rebar (#4 at 18 in) | 1,245 lin ft = 63 × 20-ft sticks, 117 chairs |
| Or wire mesh (6x6) | 24 sheets of 5 × 10 ft, about $288 – $480 |
| Vapor barrier | 864 sq ft plus 6 in laps |
| Control joints | 6 panels of about 12 × 12 ft: 84 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 |
- Plan truck access to at least two sides, or budget for a line pump.
- A three-car garage often has one taller bay for a pickup or boat; keep the slab level across the bays and slope it to the doors.
- Mark control joints between the bays so they line up with the door openings.
Pour Day for a 24x36 Slab
- Crew time: about 30 crew-hours to set forms, place, finish and cut joints (0.035 h per sq ft for a broom finish).
- Trucks: 14.75 yd³ is 2 trucks, about 74–118 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 24x36 Slab
The calculator below starts at 24 × 36 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.
24x36 Slab Questions
About $6,260 to $11,170 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 $2,580 to $3,970. Site prep and a gravel base add about $1,210 to $2,850.
At 4 inches thick with 10% waste: 528 bags of 80-lb mix, 704 bags of 60-lb mix or 1,056 bags of 40-lb mix. At 5 inches: 660 bags of 80-lb mix.
At 4 inches, 10.67 cubic yards (order 11.75 with waste); at 5 inches, 13.33 (order 14.75); at 6 inches, 16.00 (order 17.75). Ready-mix is sold in quarter yards, so round up.
Ready-mix. 14.75 yards delivered costs about $2,333, while 660 bags would cost about $4,365 and take roughly 26 hours of mixing. Bags only win below about 1.3 cubic yards.
A #4 grid at 18 inches each way needs about 1,245 linear feet of bar including laps: 63 twenty-foot sticks and about 117 chairs. Welded wire mesh instead takes 24 sheets of 5 x 10 ft.
At 5 inches thick, 13.33 cubic yards net and 14.67 with waste, so order 14.75 yards in 2 trucks. At 4 inches it is 10.67 yards net.