How many gallons is my hot tub?
How many gallons is my hot tub? Most inflatable tubs take 177 to 297 gallons, or 669 to 1,123 litres. Most hard tubs take 205 to 503 gallons, or 777 to 1,904 litres. To get your own number, measure the inside of the tub, then divide the cubic inches by 231.
Choose your shape and units, then enter the inside sizes to get the gallons.
- 1 US gallon
- 231 cubic inches
- 1 US gallon
- 3.785 litres
- Inflatable tubs, 2 to 7 seats
- 177 to 297 gal (669 to 1,123 L)
- Hard tubs, 2 to 8 seats
- 205 to 503 gal (777 to 1,904 L)
How many gallons is my hot tub? The formulas
Measure the distance between walls inside the tub, and be sure to measure water depth rather than wall height. Apply the formula matching your shape; NIST Handbook 44 defines 1 US gallon as 231 cubic inches, or 3.785 litres.
| Shape | Inches to US gallons | Centimetres to litres |
|---|---|---|
| Round | Calculate using: depth × r × r × 3.14 ÷ 231 | Calculate using: depth × r × r × 3.14 ÷ 1,000 |
| Square | side x side x depth ÷ 231 | side x side x depth ÷ 1,000 |
| Rectangle | length x width x depth ÷ 231 | length x width x depth ÷ 1,000 |
The letter r stands for radius, which is half the width of a round tub. If you measure with a centimetre tape, a hot tub volume calculator will show litres first. Divide that result by 3.785 to get US gallons.
For the Bestway SaluSpa Hot Springs AirJet 4, 52 in (132 cm) is the inside width and 26 in (66 cm) is the height. Filled right up to the rim, it would take about 239 gallons (26 x 26 x 26 x 3.14, divided by 231). Bestway shows 177 gallons (669 litres) since filling stops at the marked level.
Gallons by seat count: 2, 4, 5, 6, 7 and 8 person hot tubs
Seat counts serve only as a rough estimate. According to manufacturer specs, six seat tubs alone vary between 205 and 380 gallons (778 to 1,439 litres). Small tubs mostly sell as 2 to 4 person models, which is why the table gives 2 and 4 seats one shared row.
| Seats | Inflatable | Hard shell |
|---|---|---|
| 2 to 4 | The Lay-Z-Spa Miami, Bestway SaluSpa, MSpa Carlton, and Intex PureSpa 4 all fall between 177 and 210 gal (669 to 795 L). | Both hold 205 to 245 gallons (777 to 925 L): Master Spas TS 240X and Hot Spring Jetsetter |
| 5 | None listed | Master Spas TS 67.25 and the TS 6.2 hold 240 to 250 gallons (909 to 947 L). |
| 6 | 205 to 290 gallons (778 to 1,098 L) each in the Lay-Z-Spa Ibiza, MSpa Meteor, Intex PureSpa 6 | 305 to 380 gal, or 1,155 to 1,439 L, each in the Jacuzzi J-335, Hot Spring Vanguard, and the Master Spas TS 7.2 and the TS 8.2 |
| 7 | 297 gal (1,123 L), Lay-Z-Spa Helsinki | Each holds 305 to 455 gallons (1,155 to 1,725 L): the Master Spas TS 7.25 and the TS 8.25, plus Hot Spring Grandee |
| 8 | None listed | 503 gal (1,904 L), Bullfrog A8 |
So how many gallons in a 6 person hot tub? Expect roughly 205 to 290 for an inflatable model, or 305 to 380 for a hard shell. Check your manual or data plate for the exact number.
What is the gallon capacity for a 7x7 or 8x8 hot tub?
Outside dimensions for a 7x7 hard tub are roughly 84 in (213 cm) square, while an 8x8 measures about 94 in (239 cm). Because walls and cabinets count toward outside size, tubs appearing equal in size may hold quite different water amounts.
| Model | Outside size | Gallons (litres) |
|---|---|---|
 Master Spas Twilight TS 7.2 and TS 7.25 | 84 x 84 in (214 x 214 cm) | 305 gal (1,155 L) |
 Jacuzzi J-335 | 84 x 84 in (213 x 213 cm) | 350 gal (1,325 L) |
 Hot Spring Vanguard | 87 x 87 in (221 x 221 cm) | 375 gal (1,425 L) |
| Master Spas Twilight TS 8.2 | 94 x 94 in (239 x 239 cm) | 380 gal (1,439 L) |
| Master Spas Twilight TS 8.25 | 94 x 94 in (239 x 239 cm) | 395 gal (1,496 L) |
 Bullfrog A8 | 94 x 94 in (239 x 239 cm) | 503 gal (1,904 L) to the fill line |
So a 7x7 hot tub takes roughly 305 to 375 gallons, or 1,155 to 1,425 litres. An 8x8 takes roughly 380 to 503 gallons, or 1,439 to 1,904 litres.
Comparing inflatable and hard shell types
Since inflatables feature straight walls and flat floors, the round formula provides a close estimate. First measure the inside width, then check the water depth at the fill line.
Hard shells are harder to calculate. Seats, steps, and footwells occupy space, meaning the box formula calculates too many gallons. Rely on the manual or spec sheet for the manufacturer's number whenever possible.
Manufacturers do not all measure to the same water level. The Jacuzzi spec handbook shows 530 gallons (2,006 litres) for the J-275 when full, yet only 420 gallons (1,590 litres) when filled to an average level. Bullfrog lists the A8 503 gallons (1,904 litres) up to its fill line, or 644 gallons (2,438 litres) at maximum fill.
What is the gallon capacity of a swim spa?
You swim against a current in a swim spa, which is a long and deep tub. Expect about 925 to 2,350 gallons from the models below, several times a hot tub's capacity. That's 3,502 to 8,896 litres.
| Model | Outside size | Gallons (litres) |
|---|---|---|
| H2X Therapool SE | 132 x 94 in (336 x 239 cm) | 925 gal (3,502 L) |
| Endless Pools R200 | Dimensions are 12 ft by 89 in (366 x 226 cm). | 1,335 gal (5,054 L) |
| H2X Trainer 15 | 180 x 94 in (458 x 239 cm) | 1,380 gal (5,224 L) |
| Endless Pools E500 | 15 ft by 7 ft 5 in (457 by 226 cm) | 1,735 gal (6,567 L) |
| H2X Trainer 19D MAX | 231 x 94 in (587 x 239 cm) | 2,350 gal (8,896 L) |
You can also use the volume calculator above for a swim spa. Select the rectangle shape and type in the inside length, inside width, and water depth. Steps, seats and swim jets occupy space, making the result slightly high. Rely on the manufacturer's figure for chemical doses if you have it.
Why you need your gallon count
Each chemical dose is worked out per gallon. Type your number into the chemical calculator. Use the same figure for the startup chemicals when you fill the tub fresh.
Water weight depends on gallons too; the USGS states one gallon weighs 8.34 lb (3.8 kg). Before placing your tub on a deck, check how much your tub weighs full.
Common questions
What is the gallon capacity of a swim spa?
H2X and Endless Pools make the swim spas we checked; they hold about 925 up to 2,350 gallons, or 3,502 to 8,896 litres. More water fits as the swim spa gets longer and deeper.
How many gallons in a 6 person hot tub?
Inflatable tubs with six seats run about 205 to 290 gallons, or 778 to 1,098 litres. Hard tubs with six seats from Jacuzzi, Hot Spring and Master Spas take roughly 1,155 to 1,439 litres, or 305 to 380 gallons of water.
How many gallons are in a 4 person inflatable hot tub?
Both Lay-Z-Spa's Miami and Bestway's SaluSpa Hot Springs AirJet 4 hold 177 gallons (669 litres). The Intex PureSpa for 4 people holds 210 gallons (795 litres).
How do you change litres into gallons?
To get US gallons, divide litres by 3.785. About 264 US gallons fits in a 1,000 litre tub.
Why is the number I measured higher than the manufacturer's?
In a hard tub, the seats and the footwell take up room, and manufacturers often count the water only up to the fill line. Rely on the manufacturer's figure if you have it.