A hot tub on a deck looks like the obvious spot: close to the door, off the grass, level with the house. The problem is weight. A filled spa is one of the heaviest things most people ever put on a deck.
This article covers how to check the load before you order. For the rest of the hot tub decisions, start with the hot tub buying guide.
Short answer: every spa we have weights for puts more than 40 lbs on each square foot when filled, and 40 psf is what a standard residential deck is designed for. Plan on an engineer’s check or a ground-level pad.
What a deck is designed to carry
The American Wood Council publishes DCA 6, a prescriptive guide for building residential wood decks. It says the joists, beams, and connections in the guide are sized for a uniformly distributed live load of 40 pounds per square foot (psf), plus 10 psf of dead load for the deck’s own weight. The Council also notes that the International Residential Code requires 40 psf for decks.
Then comes the line that matters here. In the Council’s own words, “concentrated loads such as those created by hot tubs are beyond the scope of DCA 6 and require a design professional or other approved installation approach.”
So a deck built to the standard guide was not designed with a spa in mind. Local codes can differ, and an older deck may not meet today’s standard at all.
How to work out the load
You need two numbers from the spa’s listing: the filled weight and the footprint.
- Find the filled weight. If the listing only gives dry weight and gallons, multiply the gallons by 8.34 and add the dry weight.
- Multiply the length by the width in inches, then divide by 144 to get square feet.
- Divide the weight by the square feet.
- Add the bathers and divide again.
Here is a worked example with the AquaRest Discover Premium 600. It holds 240 gallons, which is about 2,002 lbs of water. Add the 295 lb dry weight and you get about 2,297 lbs. The 78 x 78 inch shell covers 42.25 sq ft. That is about 54 psf before anyone gets in.
Seven spas compared
| Spa | Filled weight | Footprint | Load before bathers |
|---|---|---|---|
| AquaRest Discover Premium 300 | about 1,566 lbs | 37.8 sq ft | about 41 psf |
| AquaRest Discover Standard 400 | about 1,825 lbs | 34.4 sq ft | about 53 psf |
| AquaRest Discover Premium 600 | about 2,297 lbs | 42.3 sq ft | about 54 psf |
| Hot Spring Mini | 1,655 lbs | 26.5 sq ft | about 62 psf |
| Coleman SaluSpa | 1,938 lbs | 27.5 sq ft | about 70 psf |
| Hot Spring Azure | 3,020 lbs | 36.8 sq ft | about 82 psf |
| LifeSmart LS100DX | 2,698 lbs | 30.6 sq ft | about 88 psf |
Filled weights for the Hot Spring, Coleman, and LifeSmart spas are from their listings, checked September 2026. The AquaRest figures are our arithmetic from listed gallons and dry weight. The Coleman footprint assumes a 71-inch circle.
Here’s what the spec sheet won’t tell you. The smallest spa is not the lightest load. The 2-person Hot Spring Mini puts more on each square foot than the 6-person AquaRest, because its weight sits on a smaller base.
Add the people
The table stops before anyone gets in. As an illustration, four adults at 175 lbs each add 700 lbs. On the Hot Spring Azure that takes the total to about 3,720 lbs, or about 101 psf. That is two and a half times the 40 psf standard.
What to do about it
- Put it on the ground. A level concrete pad next to the deck carries the load without relying on the framing. You can still step from the deck into the spa.
- Get the deck checked. A structural engineer can tell you what your deck carries now and design the extra posts, beams, and footings if it falls short.
- Ask about a permit. Your building department may require one for a spa on a raised structure. Ask before the delivery date is set.
- Check the delivery path. The route to a deck often includes stairs or a narrow side yard.
My rule of thumb: if you can walk under the deck, don’t put a spa on it without an engineer’s letter.
Balconies and roof decks
The same arithmetic applies, and the stakes are higher. Ask the building owner or a structural engineer first. An inflatable spa is not an exception: it is lighter to carry in, but nearly as heavy once filled.
To see how three spas at different prices compare, read our hot tub comparison.
Bottom line: work out the pounds per square foot before you fall for the photos. If the answer is above what your deck was built for, the spa goes on a pad or the deck gets engineered.
Sources
- Showalter J. and Ross L. (American Wood Council), “Residential Wood Deck Design,” STRUCTURE magazine, April 2017: awc.org
- American Wood Council, FAQ on the 40 psf live load in DCA 6, September 30, 2021: awc.org
- U.S. Geological Survey, “Water Density” (a gallon of water weighs about 8.34 lbs), accessed October 2, 2026: usgs.gov
- AquaRest, Hot Spring, Coleman, and LifeSmart listings (gallons, dry and filled weight, dimensions), checked September 2026