A filled hot tub weighs more than a small car, spread over a few square metres. On a concrete slab that does not matter. On a timber deck it matters a lot. Do the sum before you decide.
The sum
Filled weight = water + tub + people
- Water: 1 litre weighs 1 kg. So the litres the maker publishes are also the kilograms.
- Tub: the empty weight from the listing.
- People: we use 80 kg per adult as a round figure. Use your own.
Then divide by the footprint to get the load per square metre:
- Round tub: area = 3.14 × (half the width)²
- Square tub: area = length × width
Six worked examples
We only use tubs whose makers publish the water volume. When the empty weight is missing, we say so.
Aoxun 208 cm
- Water: 1,000 litres = 1,000 kg
- Tub: 28 kg
- Six adults: 6 × 80 = 480 kg
- Total: 1,000 + 28 + 480 = 1,508 kg
- Footprint: round, 208 cm across, so 3.14 × 1.04 × 1.04 = 3.40 m²
- Load: 1,508 ÷ 3.40 = about 444 kg per m²
Lay-Z-Spa Boracay
- Water: 669 kg. Tub: 33.9 kg. Four adults: 320 kg.
- Total: 669 + 33.9 + 320 = 1,022.9 kg
- Footprint: round, 180 cm, so 3.14 × 0.9 × 0.9 = 2.54 m²
- Load: about 402 kg per m²
Wave Tahoe 4
- Water: 650 kg. Tub: 29.5 kg. Four adults: 320 kg.
- Total: 650 + 29.5 + 320 = 999.5 kg
- Footprint: round, 156 cm, so 3.14 × 0.78 × 0.78 = 1.91 m²
- Load: about 523 kg per m²
The smallest tub gives the highest load per square metre, because the weight sits on a smaller patch.
Arebos Barcelona 6
- Water: 910 kg. Tub: 25 kg. Six adults: 480 kg.
- Total: 910 + 25 + 480 = 1,415 kg
- Footprint: square, 1.85 × 1.85 = 3.42 m²
- Load: about 413 kg per m²
Intex PureSpa Bubble 8
- Water: 1,340 kg. Tub: 45.2 kg. Eight adults: 640 kg.
- Total: 1,340 + 45.2 + 640 = 2,025.2 kg
- Footprint: round, 236 cm, so 3.14 × 1.18 × 1.18 = 4.37 m²
- Load: about 463 kg per m²
MSpa Tuscany
- Water: 1,100 kg. Tub: 75 kg. Six adults: 480 kg.
- Total: 1,100 + 75 + 480 = 1,655 kg
- The Tuscany is octagonal, 193 cm across, so its footprint is smaller than a 193 cm square (3.72 m²). Even on that larger square the load comes to 1,655 ÷ 3.72 = about 445 kg per m², and the real figure is higher.
The summary table
| Hot tub | Water | Tub | People | Filled weight | Per m² |
|---|---|---|---|---|---|
| Wave Tahoe 4 | 650 kg | 29.5 kg | 4 × 80 | 999.5 kg | about 523 kg |
| Lay-Z-Spa Boracay | 669 kg | 33.9 kg | 4 × 80 | 1,022.9 kg | about 402 kg |
| Arebos Barcelona 6 | 910 kg | 25 kg | 6 × 80 | 1,415 kg | about 413 kg |
| Aoxun 208 cm | 1,000 kg | 28 kg | 6 × 80 | 1,508 kg | about 444 kg |
| MSpa Tuscany | 1,100 kg | 75 kg | 6 × 80 | 1,655 kg | over 445 kg |
| Intex PureSpa Bubble 8 | 1,340 kg | 45.2 kg | 8 × 80 | 2,025.2 kg | about 463 kg |
When the maker does not publish the empty weight (the Wave Garda 6, MSpa Denver and MSpa Aero Plus), you can still add water and people. The Garda 6 with 1,100 litres and six adults already reaches 1,580 kg before the tub itself.
What a deck can take
UK building standards design a normal domestic floor for about 1.5 kN per m², which is roughly 150 kg per m². Every tub above puts down around three times that or more. Many garden decks are built lighter than an indoor floor, not stronger.
So the honest answer: an ordinary garden deck is not built for a filled hot tub. A deck can carry one if a structural engineer or experienced builder designs it for that load, usually with extra joists, closer spacing and posts on proper footings under the tub.
If you want the tub on a deck
- Get the deck checked or designed for the filled weight you worked out above. Give the builder your figure.
- Put the tub over the posts, not in the middle of a long span.
- Consider a cut-out: build the deck around a tub that stands on a slab below. You get the deck look and a solid base.
- Raised decks and balconies need an engineer. No exceptions.
Quick answers
Does the water level drop when people get in? It rises, which is why you fill below the top line. The total weight is still water plus people, as long as nothing spills.
Is a roof terrace or balcony OK? Only with a structural engineer's sign-off.
What is the safest base? A level concrete slab or well-laid paving. See hot tub base options and where to put a hot tub.
Choosing a size? Compare the best 4-person and best 6-person tubs.
