8x8 Concrete Slab: Cost, Yards & Bags of Concrete
Quick answer: an 8 × 8 ft slab (64 sq ft) 4 inches thick needs 0.79 yd³ of concrete, 0.87 yd³ with 10% waste (order 1 yd³ of ready-mix) or 40 bags of 80-lb mix. Installed, it costs about $590 – $990 ($9.00 – $15.50 per sq ft); DIY materials run $320 – $420.
An 8 × 8 ft pad is the usual footprint for a two- to four-person hot tub, a standby generator or a pair of heat-pump condensers. At 64 sq ft it is a small pour, 40 bags of 80-lb mix, but it carries a heavy, concentrated load: a filled 7 × 7 ft tub with people in it puts roughly 100 lb on every square foot. The base and a level top matter more here than on a patio of the same size.
Concrete for an 8x8 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) | 0.79 yd³ | 0.87 yd³ | 1 yd³ | 40 | 53 | 79 | $590–$990 |
| 5 in | 0.99 yd³ | 1.09 yd³ | 1.25 yd³ | 49 | 66 | 98 | $630–$1,030 |
| 6 in | 1.19 yd³ | 1.30 yd³ | 1.5 yd³ | 59 | 79 | 118 | $660–$1,070 |
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) | 0.79 yd³ | 36 |
| 5% | 0.83 yd³ | 38 |
| 10% | 0.87 yd³ | 40 |
| 15% | 0.91 yd³ | 41 |
Bags or a Ready-Mix Truck?
| Option | What you buy | Concrete bill |
|---|---|---|
| 80-lb bags | 40 bags at $6.50 + mixer rental $75 | $335 |
| Ready-mix | 1 yd³ at $150 + $120 delivery + $140 short-load fee | $410 |
At 0.87 yd³, bags come out $75 cheaper, mostly because a small ready-mix order pays the delivery fee and a short-load fee. The trade-off is labor: 40 bags is about 1.6 hours of mixing for a small crew with one drum mixer, and every bag weighs 80 lb. Try your own prices in the bags vs. ready-mix calculator.
What an 8x8 Slab Costs
| Line item (4 in slab) | Basis | Cost |
|---|---|---|
| Ready-mix concrete + delivery | 0.87 yd³ at $150 + $120 | $250 |
| Forms | 32 lin ft at $2.20 | $70 |
| Vapor barrier | 64 sq ft at $0.35 | $22 |
| #4 rebar at 18 in | 64 sq ft at $1.25 | $80 |
| Broom finish | 64 sq ft at $0.75 | $48 |
| Labor (place & finish) | 64 sq ft at $5.00 | $320 |
| Direct cost | Before overhead and profit | $791 |
- Installed price: $590 – $990. 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 $90 – $210 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 an 8 × 8 ft Slab
| Concrete | 1 yd³ ready-mix, or 40 × 80-lb / 79 × 40-lb bags |
|---|---|
| Gravel base (4 in compacted) | 0.91 yd³, about 1.3 tons |
| Forms | 4 × 2x4 boards 12 ft long, 12 stakes, 24 screws (32 lin ft) |
| Rebar (#4 at 18 in) | 99 lin ft = 5 × 20-ft sticks, 9 chairs |
| Or wire mesh (6x6) | 2 sheets of 5 × 10 ft, about $24 – $40 |
| Vapor barrier | 64 sq ft plus 6 in laps |
| Control joints | None needed: both sides are within the 10 ft joint spacing for 4 in |
Recommended Specs for a Hot Tub Or Equipment Pad
| Thickness | 4 in; 6 in where the tub maker asks for it (common for large or swim spas) |
|---|---|
| Strength | 3,000 PSI; 3,500 PSI air-entrained where it freezes |
| Base | 4 to 6 in of compacted crushed stone, compacted in lifts |
| Reinforcement | 6x6 welded wire mesh or #3 rebar at 18 in, on chairs |
| Surface | Dead level (no drainage slope), broom or light trowel finish |
- Read the tub or generator install guide before you pour. Most ask for at least 4 in of concrete on a compacted base; some large tubs ask for 6 in.
- Keep the top level. A patio gets a drainage slope; a hot tub pad should not, or the tub will sit out of level.
- If the electrical feed comes up through the pad, set the conduit and sweep before the pour. Cutting into a finished pad later costs more than the pad.
Pour Day for an 8x8 Slab
- Crew time: about 2 crew-hours to set forms, place, finish and cut joints (0.035 h per sq ft for a broom finish).
- 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 8x8 Slab
The calculator below starts at 8 × 8 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.
8x8 Slab Questions
About $590 to $990 installed for a 4-inch slab with forms, a broom finish and labor ($9.00 to $15.50 per sq ft), at U.S. average prices. DIY materials run about $320 to $420. Site prep and a gravel base add about $90 to $210.
At 4 inches thick with 10% waste: 40 bags of 80-lb mix, 53 bags of 60-lb mix or 79 bags of 40-lb mix. At 6 inches: 59 bags of 80-lb mix.
At 4 inches, 0.79 cubic yards (order 1.00 with waste); at 5 inches, 0.99 (order 1.25); at 6 inches, 1.19 (order 1.50). Ready-mix is sold in quarter yards, so round up.
Bags are a little cheaper here: 40 bags cost about $335 with a rented mixer, against about $410 for a 1-yard ready-mix load with delivery and short-load fees. Mixing takes about 1.6 hours for a small crew.
A #4 grid at 18 inches each way needs about 99 linear feet of bar including laps: 5 twenty-foot sticks and about 9 chairs. Welded wire mesh instead takes 2 sheets of 5 x 10 ft.
For most two- to four-person tubs, yes, on a compacted gravel base with wire mesh or light rebar. Larger tubs and swim spas often call for 6 inches; follow the maker's install guide, because the warranty can depend on it.