12×12 Concrete Slab Cost: Patio, Shed & Spa Pad Pricing

Quick answer: a 12x12 concrete slab (144 sq ft) at 4 inches thick costs about $1,130 to $1,970 installed, or $520 to $750 in materials if you pour it yourself. A plain patio sits near the low end, a shed floor with a vapor barrier and rebar near the middle, and a 6-inch hot tub pad at $1,720 to $2,160. You need 1.96 cubic yards of concrete with 10% waste, or 88 bags of 80-lb mix.

Twelve by twelve is one of the most requested slab sizes because it fits three common jobs: a small patio for a table and four chairs, a floor for a 10x12 or 12x12 shed, and a pad for a hot tub with room to step around it. Those three jobs use the same footprint but not the same slab. The thickness, the reinforcement and even whether the surface should slope are different, and that is where the price differences come from. This guide prices each one.

12x12 Slab Cost by Use

The spread between the three is smaller than people expect. Going from a patio to a spa pad adds about $147 of concrete, plus the rebar and vapor barrier. Labor, forms and delivery stay about the same, because a 6-inch slab takes the same crew the same morning to place and finish.

Cost by Thickness

Per square foot, a 4-inch 12x12 works out to $7.85 to $13.69 installed. That is a little cheaper per foot than a 10x10, because the delivery fee and the crew's setup time are spread over 44 more square feet.

Patio: What Matters for Price

A patio is the simplest of the three. Four inches is plenty for foot traffic and furniture, and IRC section R506 sets 3.5 inches as the floor-slab minimum, so 4 inches gives a little margin for uneven ground. Many patio contractors use welded wire mesh (about $0.50/sq ft) instead of a rebar grid, and skip the vapor barrier because nothing above the slab needs to stay dry.

The one thing a patio needs that the other two do not is slope. A fall of 1/8 to 1/4 inch per foot away from the house means the far edge sits about 1.5 to 3 inches lower than the edge at the wall. Set the forms to that slope before the pour; it costs nothing extra but is hard to fix later.

Finish is the big price lever on a patio. A stamped 12x12 adds roughly $970 to $1,220 to the bill at typical rates: the stamped finish runs $6.00 to $12.00 per sq ft against $0.50 to $0.80 for broom. Complex patterns, multiple colors or a crew that bills stamping at a higher labor rate (around $10.00 per sq ft instead of $5.00) push it higher. See the patio slab cost guide for the full finish comparison.

Shed Floor: What Matters for Price

A shed slab has to be flat and square more than it has to be strong. Prefab shed kits are built to sit on a level surface, so the forms should be checked with a level and the diagonals measured equal before any concrete goes in. Because the shed is closed in, a 6-mil polyethylene vapor retarder under the slab (as IRC R506.2.3 asks for under floors of enclosed spaces) keeps ground moisture from wicking up into tools and the shed's wood floor framing. On a 12x12 that adds about $50.

Set anchor bolts while the concrete is still plastic, lined up with the shed's sill plate. If a riding mower or ATV will live inside, go to 5 inches; that adds only about $73 at full scope. Our shed pad guide compares a slab with a gravel pad.

Hot Tub and Spa Pad: What Matters for Price

A filled hot tub with people in it is one of the heaviest loads a backyard slab carries, and the weight sits on a small footprint. That is why most installers pour spa pads at 6 inches with a rebar grid, and why many hot tub makers list their own pad requirements in the installation manual. Check that manual first: if it calls for a specific thickness or flatness, the manufacturer may treat a weaker pad as a warranty issue.

• Level, not sloped. A spa shell should sit flat, so set the forms level instead of sloping them like a patio. Keep the top of the pad a little above the surrounding ground so rain runs off the edges.
• Power first. Run electrical conduit through the forms before the pour if the disconnect or wiring will come up through or beside the slab. Cutting a trench in a finished pad costs far more than a length of conduit. The wiring itself is a job for a licensed electrician.
• Size. A 12x12 leaves a walkway around most residential tubs, with room for steps and a cover lifter. Measure your tub plus its steps before you set the forms.

The 6-inch pad needs 2.93 yd³ of concrete with waste, or 132 bags of 80-lb mix. At that volume a truck is the practical choice.

Bags or Ready-Mix for a 12x12?

At 1.96 yd³ for 4 inches, a 12x12 is past the point (about 1.5 yards) where a truck usually beats bags, but still well under most plants' usual minimum of 5–6 yards. So the real comparison is bags against ready-mix plus a short-load fee:

Even with a short-load fee, ready-mix is close to or below the bag price, and it saves you from mixing about 3.5 tons of concrete by hand. Bags make sense only when a truck cannot get within chute reach (about 15 to 20 ft) and a pump would cost more than the slab. Compare both with the concrete bags calculator and the ready-mix calculator.

Worked Example: 12x12 Shed Floor

The rebar grid at 18 in centers takes 11 twenty-foot #4 bars and about 25 chairs. One control joint each way splits the slab into four 6x6 panels, inside the usual limit of about 10 ft for a 4-inch slab. A contractor would quote somewhere between that direct cost and $1,972 once overhead and profit are added. If the site needs digging out and a gravel base, add $202 to $475.

DIY or Hire a Pro?

A 12x12 patio or shed floor is a reasonable first DIY slab if you have two or three helpers and the truck can reach the forms. A crew spends roughly 5 crew-hours on it, which is a long half-day for beginners. The money saved is mostly labor: the gap between the DIY materials range ($520 to $750) and the installed range. A spa pad is the one to think twice about. It has to be flat, thick and right the first time, and a rework under a filled tub is expensive. Read our DIY vs. contractor guide, and run any quote through the quote checker.

Other sizes: 10x10, 20x20 and 24x24, or price your exact dimensions in the slab cost calculator.

Sources and Method

Volumes use length × width × thickness with published bag yields. Costs use the same line items and default rates as our calculator (see the methodology); they are working benchmarks and vary by region and season. Thickness, vapor retarder and base guidance follow the International Residential Code (section R506) and ACI 302.1R. Hot tub pad requirements come from each manufacturer, so their installation manual has the final word.