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SlabCosts
Prices updated January 2026

15×15 Concrete Slab Cost

A 15×15 slab covers 225 square feet. Here's the concrete, bags and cost for 2026 — a common size for a patio.

Concrete (4", waste in)

3.06 yd³

138 × 80 lb bags

Materials (ready-mix)

$442 – $756

delivered, 4" slab

Installed by a pro

$1,238 – $2,700

4" slab, national average

15×15 slab cost calculator

Adjust thickness, waste or region — the cost updates live.

Waste & region

Order extra for spillage & uneven subgrade. 10% is typical.

Installed cost estimate

$1,238 – $2,700

225 sq ft · 3.06 yd³ concrete

Bags of concrete needed (rounded up)

138

80 lb

184

60 lb

220

50 lb

275

40 lb

Ready-mix (delivered)
$442 – $756
Bagged mix (80 lb, DIY)
$759 – $1,242
Installed by a pro
$1,238 – $2,700

Estimate only — not a quote. Bag counts are rounded up and include a 10% waste allowance.

Installed $1,238 – $2,700

15×15 slab cost by thickness

Thickness Concrete 80 lb bags Ready-mix Installed
4" 3.06 yd³ 138 $442 – $756 $1,238 – $2,700
5" 3.82 yd³ 172 $537 – $901 $1,406 – $2,869
6" 4.58 yd³ 207 $633 – $1,046 $1,575 – $3,038

Includes a 10% waste allowance; bag counts rounded up. National US averages, January 2026.

You'll also need

Sized for this exact slab — tap any item to open its calculator with your measurements already filled in.

Gravel base

3.19 yd³

4" compacted base under the slab

≈ $96 – $208

Open calculator
Rebar

17 sticks

#4 bar, 18" grid (22 bars)

≈ $119 – $221

Open calculator
Bedding sand

0.69 yd³

~1" leveling layer

≈ $19 – $40

Open calculator

15×15 concrete slab: what to expect

A 15×15 slab covers 225 square feet. At the standard 4" thickness it takes about 3.06 cubic yards of concrete once you allow 10% for waste, which is roughly 138 × 80 lb bags if you mix by hand. Stepping up to 6" — sensible if it'll carry a vehicle — raises that to about 4.58 cubic yards.

Budget around $1,238 – $2,700 to have a 4" slab this size poured and finished by a contractor, or roughly $442 – $756 in ready-mix if you're doing the labor yourself. On top of the concrete you'll need about 3.19 yd³ of gravel base and 17 sticks of rebar.

Compare nearby sizes

Planning something bigger or smaller? Jump straight to the cost for a nearby size.

Size Concrete (4") 80 lb bags Installed cost
12×16 2.61 yd³ 118 $1,056 – $2,304
14×14 2.66 yd³ 120 $1,078 – $2,352
10×20 2.72 yd³ 123 $1,100 – $2,400
16×16 3.48 yd³ 157 $1,408 – $3,072
12×24 3.91 yd³ 176 $1,584 – $3,456
16×20 4.35 yd³ 196 $1,760 – $3,840

See all common slab sizes →

Prices updated January 2026 National US averages · reviewed quarterly

Volumes use standard bag yields and a 10% waste allowance; costs are national US averages that vary by region, mix and finish. See our methodology for exactly how each figure is worked out, or check the reference sources:

Slab cost by project

Concrete Slab Cost Cost per sq ft + calculator Garage Slab Cost Typical 20×20 / 24×24 Driveway Slab Cost Concrete vs asphalt Patio Slab Cost 10×10 to 20×20 Shed Base Cost Small pads

Frequently asked questions

How much does a 15×15 concrete slab cost?
A 15×15 slab (225 sq ft) costs about $1,238 – $2,700 installed at 4" thick in 2026, or $1,575 – $3,038 at 6". DIY in materials, the ready-mix runs about $442 – $756 at 4".
How many yards of concrete for a 15×15 slab?
At 4" thick a 15×15 slab needs about 3.06 cubic yards including 10% waste (2.78 yd³ net). At 6" it needs about 4.58 cubic yards.
How many bags of concrete for a 15×15 slab?
At 4" you'd need roughly 138 × 80 lb bags, 184 × 60 lb bags or 275 × 40 lb bags. That's a lot of mixing — past about a cubic yard, ready-mix is usually cheaper and easier.
What base and rebar does a 15×15 slab need?
Plan on about 3.19 cubic yards of compacted gravel base and roughly 17 sticks of #4 rebar on an 18" grid. The "You'll also need" cards size these for you.