# Round vs square inflatable hot tubs

Source: https://bubbleandsoak.co.uk/blog/round-vs-square-inflatable-hot-tub
Published: 2026-10-12
Publisher: Bubble and Soak

**In short:** At the same outer width, a square tub has more inside area than a round one, about 27% more, so it offers more legroom and holds more water. Square tubs fit neatly into corners and against fences. Round tubs are the most common, cheapest to make and often lighter, and they suit open lawns or patios with space all round.

Shape is one of the first choices with an inflatable hot tub, and it matters more than it looks. A square tub and a round tub of the same width do not hold the same water or give the same room. They also sit differently on a patio: a round tub leaves awkward gaps in a corner, while a square tub can tuck against two fences. This guide works out the space and water for both shapes, compares two models from our guides and covers covers and bases.

## The geometry in plain terms

A circle fills about 79% of the square that surrounds it. So if a round tub and a square tub have the same inner width, the square one has about 27% more floor area and, at the same depth, about 27% more water. Those corners also give room to stretch out or sit diagonally.

You can work out any tub's volume with our [water volume calculator](https://bubbleandsoak.co.uk/tools/water-volume-calculator). For a round tub, litres equal pi times the inner radius squared times the depth, all in centimetres, divided by 1,000. For a square tub, multiply inner length by width by depth and divide by 1,000.

## Worked example

Take an inner width of 150 cm and a water depth of 55 cm. These are illustration figures, not a particular model.

| Shape | Sum | Water |
| --- | --- | --- |
| Round, 150 cm inner diameter | 3.1416 x 75 x 75 x 55 / 1,000 | About 972 L |
| Square, 150 x 150 cm inner | 150 x 150 x 55 / 1,000 | About 1,238 L |

Water litres at the same inner width and depth

1. Measure or look up the inner width, not the outer size.
2. Take the water depth from the manual's fill line.
3. Use the sums above or the calculator to get litres.
4. Add about 1 kg per litre, plus the tub and bathers, to find the filled weight for the base.

## Two models side by side

Here is a round and a square Lay-Z-Spa from our guides, using listing figures.

| Fact | Lay-Z-Spa Milan AirJet Plus | Lay-Z-Spa Hawaii HydroJet Pro |
| --- | --- | --- |
| Shape | Round | Square |
| Outer size | 196 x 71 cm | 180 x 180 x 71 cm |
| Water | 916 L | 795 L |
| Seats | 6 | 6 |
| Jets | 140 AirJet Plus | 148 HydroJet and AirJet |
| Weight empty | 38 kg | 54.3 kg |

Round and square Lay-Z-Spa listing facts

[Compare Lay-Z-Spa models](https://bubbleandsoak.co.uk/best/lay-z-spa-models-compared)

## Fitting the tub to your garden

Square tubs suit corners, decking edges and narrow patios, because they sit flush against straight lines and waste less space. A round tub in a corner leaves triangles of unused ground either side, but round tubs are easier to place on an open lawn or a patio with space all round, and they are the most common shape, so there is more choice.

Whatever the shape, leave enough room to walk round the tub, reach the pump unit and lift the cover off. Keep the tub well clear of fences you need to maintain and of overhanging branches that drop leaves into the water.

## Covers and bases

Covers are shape specific. Square covers can be harder to seal at the corners, so check the fit and the straps. Round covers are widely sold in standard sizes. Thermal cover upgrades are available for both shapes from several makers.

The base must be level and strong enough for the filled weight. A square tub of the same width holds more water and so puts more load on the base. See our [base ideas article](https://bubbleandsoak.co.uk/blog/inflatable-hot-tub-base-ideas) for patio, decking and gravel options.

Note: Have decking checked by someone qualified to judge its load before placing a filled hot tub on it.

## Heating, chemicals and running energy

More water takes more energy to heat. Using the worked example, warming 972 litres from 10 to 38 °C needs at least about 32 kWh, while 1,238 litres needs at least about 40 kWh, before any heat loss. On a 2.2 kW heater that is roughly 14.4 hours against 18.3 hours. Try your own tub in the [heat-up calculator](https://bubbleandsoak.co.uk/tools/heat-up-calculator).

Chemical doses also scale with litres, so a larger square tub needs a little more sanitiser and balancer each week. Always dose from the water volume in your manual and follow the chemical maker's instructions. Shape itself does not change heat loss much; the cover, wind and air temperature matter far more.

## Frequently asked questions

**Is a square hot tub bigger inside?** At the same width, yes, about 27% more floor area and water than a round tub.

**Do square tubs take longer to heat?** If they hold more water, yes. Heat-up depends on litres and heater kW, not shape as such.

**Which shape is easier to cover?** Round covers are simpler and more widely sold. Square covers need a good fit at the corners.

**Which shape fits a small patio?** A square tub against a wall or in a corner often uses a small patio best.

## Buying guides on this topic

- https://bubbleandsoak.co.uk/best/best-2-to-4-person-inflatable-hot-tubs
- https://bubbleandsoak.co.uk/best/best-6-person-inflatable-hot-tubs
- https://bubbleandsoak.co.uk/best/lay-z-spa-models-compared