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How Many Gallons Are In A Hot Tub? (Measuring Calculator Inside)

If you own a hot tub then knowing its capacity is essential. Not only does it help you determine how many people can be in your hot tub at once, but also when cleaning your tub, knowing its proper measurements is very important. So, how do you determine how many gallons are in a hot tub

A 2-person hot tub may hold 150 to 220 gallons of water. The ones for 3-4 people generally have about 285 gallons, and a tub for 6 people and above has 300 to 485 gallons. There are also larger ones that can hold up to 8 people and contain around 600 gallons of water.

There are two methods of calculating how many gallons are in a hot tub. The timed filling method is by far the simplest one, or you could try calculating it by the dimension of the tub with a little bit of math. I’ll discuss the process of each method step by step in the following section.

Measuring a Hot Tubs Capacity

The fastest way of finding a hot tub’s water capacity is by looking up the user’s manual. Most manufacturers should list the specifics of their tub in the manual. But if you lost the manual, or bought it from a second-hand dealer, then you got to calculate it manually.

As I said earlier, there are two ways of measuring the water capacity of a hot tub. I’ll start with the easiest one. It has the most amount of math involved, but it is pretty easy contrary to what you would expect. Without further ado, let’s get started,

Method 1: Calculate the Dimension of The Tub

As the name suggests, this method is pure calculations and measurements. The hardest part is taking accurate measurements because the math is pretty easy once you know the formula. Here are the tools you’ll be needing:

  • A measuring tape
  • A calculator
  • A notepad

As you can see, you don’t need a whole lot of stuff to complete this process. You should probably keep your phone nearby, too, if you are a dummy when it comes to math like me. This method varies a bit depending on the shape of the hot tub, so pay attention. 

Round Tub

Round tubs are a fair bit different from square ones. You need to measure the diameter of the tub instead of the width. Place the tape measure on one side and stretch it to the other side through the middle of the tub.

Now, measure the depth by placing the tape measure vertically along the side of the tub. Note both numbers down and multiply it as diameter x diameter x depth. Then, you need to divide the result by 1728 to get the water capacity. 

You will need to multiply the final result with 2.4 for tub’s that have seats and 4.8 for the ones without seats. The resulting figure will be your tub’s capacity in gallons. 

Based on the material of your tub the calculation can be slightly different. Here I’ll be discussing acrylic and wooden tubs. 

Acrylic Round Tubs

For acrylic round tubs, you need to have the diameter of the tub along with its height. Keep in mind that this measurement is for inches. After you measured the diameter and height with the measuring tape, you need to use the following equation.

 Estimated Volume = {(Diameter x Diameter x Height / 1728 } x 2.4

Wooden Round Tubs

Wooden round tubs have a different sort of calculation for measuring out the volume. Usually, for the same diameter and height, wooden tubs have twice the holding capacity of their acrylic counterpart. The following is the equation you need to use for the measurement.

 Estimated Volume = {(Diameter x Diameter x Height / 1728 } x 4.8 

Square Tub

Square tub is fairly similar to the round tub method. Instead of using a 2 x diameter, you will use length and width. Even though I’m calling it square, this method would work even if your tub is a rectangle or a parallelogram. It’s just that most tubs are perfect squares for aesthetic reasons.

Take your tape measure and note down the length and width of the tub. Like before, hold it along the sides to take the horizontal measurements or depth. Multiply depth x length x width, just like I showed with the round tub.

The rest of the process is the same as before. Divide the result by 1728 and then multiply it again with either 2.4 or 4.8.

That wasn’t so bad, now, was it? The dimension calculation method is the easiest thing in the world as long as you know the formula. However, this method won’t work if the shape of your tub is too odd.

Method 2: Calculate by The Filling Time

This method requires the most tools and conditional requirements but very little math. First, let’s look at the things you will need for this to work:

Steady Water Supply

The strictest requirement of this method is the water source. You would need a steady water supply with no fluctuation in the flow rate for this to work. 

The flow needs to be stable and continue at an identical pace throughout the testing duration. But, most people don’t follow this method due to the strict steady water flow requirement. 

Measured Container

The larger the container, the easier it will be for you to calculate. I prefer using a five-gallon bucket because that’s an easy number to work with.

The larger the container the easier it will be for you to calculate. I prefer using a five-gallon bucket because that’s an easy number to work with. You would also need a stopwatch to calculate the time, so grab your phone and get ready. 

You must first fill the gallon container with a hose and start the timer. Then note down the time it took to fill the thing. Then you have to start filling the hot tub with the same hose, with the same water flow rate and note the time down as before. Finally you have to use your findings to measure the approximate value of the hot tub volume. 

To put it more simply, here is a step by step explanation of how to do it. Follow this and you will calculate your hot tub volume in no time. 

Step 01: Get the water source running to fill up the tub. You can use a garden hose for this purpose, as they can fill up the tub pretty quickly.

Step 02: Get a stopwatch, or a phone, or anything that you can keep track of time with. Start the time when you start filling up the tub, then take a note of how much time the tub needs to be filled.

Step 03: After the tub is full to the brim, stop the hose. Stop the time and record the fillup time for the tub.

Step 04: Collect your one-gallon container and get the timer ready. Start your water source to start filling up the gallon. Make sure it has the same pressure as before, or it will mess up the whole calculation.

Step 05: Stop the timer after the jug is filled up with water. Now you can move onto calculation to figure out the approximate volume of the tub.

Step 06: Convert both fill-up time for tub and gallon into seconds. Suppose, it took 5 minutes to fill up the tub. The total time would be 5×60 = 300 seconds. And it took 30 seconds to fill up the 1-liter gallon. 

So, the approximate volume of the tub = (Time to fill the hot tub in seconds / Time to fill the one liter gallon)

How Big of a Hot Tub Do You Need?

Shopping for a good hot tub can be challenging for people who have no experience with it. People often get the wrong tub size because they fail to estimate their activity range.

Hot Tub For 2-3 People

The hot tub for 2- 3 people is the smallest tub size manufactured throughout the world. Round ones should have a diameter of about 5’5” to 6’9”. The square ones should also have a width and length around that range.

These tubs generally hold around 150 to 200 gallons of water. For small families, this is the ideal size for hot tubs, unless you have friends that like to join often.

Hot Tub For 4-5 People

Tubs for more than 3 people need to be a bit larger than the 2 people tub. Generally, these tubs have a range of 6’5” to 7’5”. A tub of this size range can easily fit up to five people while leaving enough space for movement.

These tubs can hold anywhere from 180 gallons to 3000 gallons of water. People looking for small parties and gatherings should get something around this range.

Hot Tub For 6+ People

Everything starts to get supersized from this point on. The tubs in this category have an average measurement of 6’9” to 8’8”. These are fairly large and can accommodate up to 8 people.

This size range is for people looking for luxury or looking to throw a big party, or maybe both. You would need a lot of water to fill these bad boys though, as even the smallest ones can hold up to 400 gallons.

I believe you can now accurately calculate how many gallons are in a hot tub with or without the help of a calculator. The dimension calculation is the safest and the most accurate method because the filling time method has too many unreliable variables. I hope this article is of help to you. Thanks for stopping by. 

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Written by Ferdi Vol
Ferdi Vol is a pool and hot tub owner who has been working in this industry for over 5 years. He has learned all the ins and outs of maintaining pools and hot tubs, as well as how to privately own one. Ferdi Vol is also passionate about blogging, researching topics that he shares with his readers online via this blog.
About Ferdi Vol
About Pool Uncle
Pool Uncle is a blog that focuses on helping pool and hot tub owners get the right tools, maintain their pools and hot tubs, and learn about how to care for them. It provides readers with all of the information they need to keep their pools clean, safe, and looking great. The website also publishes original articles about pool maintenance topics such as filtration systems or algae prevention techniques.
About the Author
Ferdi Vol has been in the swimming pool and hot tub as an owner for over 5 years. His experience ranges from owning a pools and hot tubs and maintaining them. He’s learned about pumps, filters, chemicals, cleaning products, treatment systems… you name it!
About Ferdi Vol
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