Small and plunge pool cost in St. Louis

A small or plunge pool in the St. Louis area typically costs about $45,000–$80,000 installed. That surprises people, because a 10×20 pool has about 40% of the water area of a 16×32. Most of a pool's cost is excavation, equipment, electrical, permits and the fence, and those barely shrink. Where small pools do win is running cost, small yards and spa-style heating.

Small fiberglass, installed: About $45,000–$80,000
Missouri dealers' smallest category: $75,500 average, turnkey
Precast concrete plunge, installed: About $42,000–$69,000
Shipping-container pool, installed: About $50,000–$85,000+
Heat a 10×20 from 60°F to 82°F: About $9 with gas

Small pool options and what they cost

Type	Installed cost	What to know
Small fiberglass pool	About $45,000–$80,000	The most common small pool. Catalog shapes from 8×14 to about 12×25, installed by local builders.
Precast concrete plunge	About $42,000–$69,000	A factory-built tiled concrete box set by crane. Soake lists $27,000–$34,000 for the pool and equipment before delivery, site work and permits. We found no installer based in St. Louis.
Shipping-container pool	About $50,000–$85,000+	A steel container lined as a pool, often set partly above ground. River Pools puts the unit at $35,000–$65,000. We found none installed in Missouri.
Small custom concrete	Near $75,000+	Any shape, but the same crew, forms and steel as a big pool. No reliable published small-pool figure.

Fiberglass from River Pools (2025) and Thursday Pools' Missouri survey (2026); precast from Soake, This Old House (2026) and Plungie's US installed figures; container from River Pools (2026).

Why half the size is not half the price

River Pools puts it plainly: excavation, equipment and labor cost about the same regardless of size. The numbers back that up.

Missouri dealers: their smallest pool category averaged about 68% of the price of their largest.
One Texas Leisure Pools dealer lists its tiny Fiji plunge at $40,127 and its 16×40 Caribbean at $72,377: 55% of the price for about a tenth of the water area.
The pump does not shrink. The national pump standard sets the same minimum class of pump and filter for any pool under 13,000 gallons, so a plunge pool gets the same equipment as a full-size one.
The fixed costs do not shrink. Plungie itemizes the costs beyond the pool itself at about $25,000–$43,000 or more: permits, installation, crane, equipment, plumbing, electrical and freight.
The fence does not shrink much. A barrier around the yard costs about the same whatever is inside it. See pool fence cost.

For comparison, full-size pools in St. Louis start around $45,000 for vinyl and $65,000 for fiberglass. A small pool saves money, just not in proportion to its size.

Small plunge pool in a landscaped back yard — Stock photography for illustration. A small pool leaves room for a deck and lawn on a tight lot.

Small fiberglass models

Model	Size	Gallons
Latham Milan 8.14	8×14, 4 ft deep	1,200
Latham Milan 10.16	10×16	2,450
Latham Milan 10.20	10×20, 4 ft 10 in deep	3,900
Latham Enchantment 9.17 / 9.21 / 9.24	9 ft wide, 17–24 ft long	3,200–4,800
River Pools N16 / R20 / D24 / I25	8×16, 10×20, 12×24, 12×25	Not published
Thursday Pools Nook	8 ft 4 in × 16 ft, 4 ft 8 in deep	Not published
Leisure Pools Palladium Plunge	8×16 and 8×20	Not published

Manufacturers do not publish prices; they quote through local builders. A 16×32, by comparison, holds roughly 19,000 gallons.

Heating and running costs

This is where a small pool pays you back. Using the St. Louis gas and electric rates from our pool heater cost page:

Compare	10×20 plunge (3,900 gal)	16×32 pool (about 19,100 gal)
Warm from 60°F to 82°F, gas	About $9, about 2 hours	About $46, about 10½ hours
Warm from 60°F to 82°F, heat pump	About $6, up to about 8 hours	About $31, up to about 40 hours
Heater size for April or October	About 59,000 Btu	About 150,000 Btu
Season at 80°F, uncovered, heat pump	About $255	About $652
Season at 80°F, uncovered, gas	About $510	About $1,307

Our arithmetic. Heat-up times use a 400,000 Btu gas heater and a 140,000 Btu heat pump (85,000 Btu in 50°F air), before heat losses. Heater sizes use the Department of Energy's sizing rule; season costs scale DOE's Kansas City estimates by surface area.

Chemicals scale with gallons too, so a 3,900-gallon pool needs about a fifth of the chlorine of a 16×32. Pump electricity falls less, because the pump is not much smaller.

Using a plunge pool as a spa

Latham notes that adding a heater often lets a cocktail pool work like a hot tub. In St. Louis that depends on the heater. Holding a 10×20 at 104°F takes roughly 130,000–166,000 Btu per hour with 35–50°F air, by DOE's sizing rule, and real losses at spa temperatures are higher. A gas heater can do that; a heat pump, at about 85,000–90,000 Btu in 50°F air, cannot. A cover makes a large difference. The CPSC says spa water should never exceed 104°F.

Permits and small yards

Permits still apply. Building codes treat anything that can hold more than 24 inches of water as a pool. The City of St. Louis exempts only pools under 24 inches deep and under 250 sq ft. A plunge pool needs a permit and a barrier everywhere in the metro.
Small lots. Kirkwood caps accessory structures at 7% of the lot or 1,500 sq ft. Town and Country keeps the pool deck 20 feet from lot lines and the water within 30 feet of the house. Lake Saint Louis limits the fenced area to 4 times the pool's surface. On tight lots these rules often make a small pool the only option.
Above-ground and container pools. The pool wall can serve as the barrier if it is at least 48 inches above ground and the steps lock or can be removed. Lake Saint Louis bans above-ground pools other than small temporary ones; Town and Country requires a conditional use permit unless at least 60% of the wall is below ground.

See pool permits by city for your city's full process.

Questions to ask a builder about a small pool

What does this pool cost compared with the next size up, line by line?
Which costs are fixed regardless of size?
What heater would you use, and can it hold spa temperature?
Does it need a crane, and is that in the price?
How will it fit my city's setbacks and lot coverage rules?

Have a small yard?

Get matched with a local builder who can tell you what fits, and what the next size up would really cost.

Get matched with a local pool builder Use the pool cost calculator

Common questions about small and plunge pools

How much does a plunge pool cost in St. Louis?

A small fiberglass pool installed in the St. Louis area typically costs about $45,000–$80,000. River Pools puts a basic small-pool install at $45,000–$75,000, and Missouri dealers' smallest category averaged $75,500 turnkey in 2026. A precast concrete plunge pool runs about $42,000–$69,000 installed.

Is a small pool much cheaper than a regular pool?

Less than you would think. Excavation, equipment, electrical, permits, the fence and delivery barely shrink with the pool. In the Missouri dealer survey the small category cost about 68% of the large one, and River Pools says a project rarely costs much less than $70,000 turnkey.

Does a plunge pool need a permit in St. Louis?

Yes. Codes treat anything that can hold more than 24 inches of water as a pool. The City of St. Louis exempts only pools under 24 inches deep and under 250 sq ft, so a real plunge pool needs a permit and a code-compliant barrier everywhere in the metro.

Can a plunge pool be heated like a hot tub?

With a gas heater, a small one can. Holding a 10×20 pool at 104°F on a cool evening takes roughly 130,000–166,000 Btu per hour, which a gas heater can supply. A heat pump cannot, since it makes only about 85,000–90,000 Btu at 50°F.

How much cheaper is a small pool to heat?

Much cheaper. By our arithmetic, a 10×20 plunge pool costs about 39% as much as a 16×32 to keep warm through a season, and warming it from 60°F to 82°F costs about $9 with gas versus about $46 for the larger pool.

What is a cocktail pool?

A small pool built for lounging and cooling off rather than swimming laps, typically about 10×16 to 10×20 feet and 3 to 5 feet deep. Latham notes that adding a heater often lets a cocktail pool work like a hot tub.

Are shipping-container pools allowed in St. Louis?

They are regulated as pools, so they need a permit and a barrier. If the wall stands at least 48 inches above ground and the steps lock or can be removed, the wall can serve as the barrier. Lake Saint Louis bans above-ground pools other than small temporary ones, and Town and Country needs a conditional use permit unless most of the wall is below ground.

Sources

Published October 27, 2026. Planning ranges, not quotes.