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How Many Gallons in a Hot Tub? 4 Ways to Figure It Out

In this article, we're going to show you how to calculate the volume of your hot tub, how much that will weigh, and give you some tips for ensuring you're planning for this weight.
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Did you know?

  • Water weighs 8.3 pounds per gallon
  • A small hot tub with 150 gallons of water weighs over 1,200 pounds

Can your deck support your hot tub?

In this article, we're going to show you how to calculate the volume of your hot tub, how much that will weigh, and give you some tips for ensuring you're planning for this weight.

Let's get started by looking at the easy ways to work out the amount of water in your tub.

How Do I Figure Out How Many Gallons My Hot Tub Holds?

Before anything else, you should ensure you know your hot tub's make, model, and manufacturer, as this will make everything else easier. Here are a few methods you can use to figure out how many gallons of water are in your tub.

1. Check Your Hot Tub Manual

The manual should always be the first thing you refer to when figuring out anything about your hot tub. Most manufacturers will provide clear directions on everything, including the tub's dimensions and water capacity.

If you do not have the physical manual, you can also search for it online, as many companies will have a digital version manual for most of their products. But, if you cannot find it, you can use one of the other methods below.

2. Call the Spa Dealership

Another easy way to determine your hot tub capacity is to call the spa dealership or store where you bought it. If the store still has the particular model in stock, they can quickly check the capacity for you.

Even if the dealership does not have the tub in stock, they have records of their previous inventories of hot tubs and swim spas, so they can still be handy.

3. Google It

Google always has an answer for almost any query you can think of, so it is also a perfect place to look for information on the gallons of water your tub can hold.

However, make sure you know the tub manufacturer, type, and model number before you start googling to ensure you get more accurate results. The serial/model number should be printed somewhere inside the hot tub's cabinet.

4. Call the Manufacturer

If you still come out empty with all the methods above, another way to determine the volume of your tub is by calling the manufacturer.

You should be able to find the manufacturer's contact details on their website if you do not already have this information.

Besides calling the manufacturer, you can also reach the company's customer support team via their social media channels. Most companies are now available on Facebook, Twitter, Telegram, and most other social media platforms.

Manually Calculating the Number of Gallons

It is also possible to determine the capacity of your hot tub by calculating it manually. Here, there are several methods you can use, but the following are the easiest and most accurate.

1. The Dimension Calculation Method

The dimension calculation method will depend on the shape of your hot tub. However, the process is relatively simple as most of the work will entail measuring the dimensions of the tub.

Here are the steps to follow.

  • Step 1: Measure the dimensions of your hot tub using a tape measure.
    • Square/Rectangular Tub Method: For a square or rectangular tub, you need to measure the length, width, and depth.
    • Round Tub Method: If you have a round tub, you should measure the radius and depth of the pool. When finding the radius, measure the distance across the center of the tub and divide that by 2.
  • Step 2: Calculate the volume using these dimensions.
    • Square/Rectangular Tub: Length x Width x Depth
    • Round Tub: Radius x Radius x Depth x 3.14
  • Step 3:  Multiply the number by 4.8 to get the gallons of water in your tub. If you have seats, you should account for this by multiplying by 3.4.

2. The Timed Fill Method

The timed fill methods can help you estimate the number of gallons in your tub. However, it is essential to note that this method will only give you a rough estimate.

You will need a hose, a 10-gallon bucket, and a stopwatch for this method. Here are the steps to follow.

  • Step 1: Turn on the water to fill up the tub and start your stopwatch. Record how long it takes to fill.
  • Step 2: Now, fill the 10-gallon bucket with water and record how long it takes to fill up.
  • Step 3: Convert the minutes it takes to fill the tub and bucket into seconds for easy calculation.
  • Step 4: Divide the time it takes to fill the tub with the time it took to fill the 10-gallon bucket with water.
  • Step 5: Multiply the number you get by 10 to get the volume of water in your tub.

How Many Gallons In a 8' x 8' Hot Tub?

An 8' x 8' tub holds between 550 and 650 gallons of water. These tubs can accommodate 8 or more, depending on the model.

How Long Does it Take to Fill a Hot Tub?

Your hot tub filling guide should provide all the information you need to know about how to fill up the tub and other things like how long it will take.

However, the fill-up time will depend on several factors, such as the size of the tub and your water pressure/flow rate. Large tubs like the 8-person ones will take the longest to fill up, while the smaller 2 or 3-person models take just a few minutes.

If your water has low pressure, you can expect the tub fill time to increase significantly. Also, the width of the hose you are using to fill the tub affects the fill time, given its impact on the flow rate.

On average, it takes between 1-hour and 1.5 hours to fill a 400 to 500-gallon hot tub. You can use this average to estimate how long it will take to fill your specific tub size.

Does Water Evaporate from Hot Tubs?

Like swimming pools and other recreational water bodies,  the water in hot tubs will evaporate. Evaporation is one of the main reasons you need to know the amount of water in your tub so that you can tell how much water to add when maintaining the hot tub.

Your hot tub's evaporation rate will depend on the specific water temperature and usage. However, it is around the same as a heated swimming pool, which is 0.085 to 0.128 gallons per square foot every day.

But how much does hot tub maintenance cost? The higher the evaporation rate, the higher the tub maintenance cost as you will have to keep refilling it often with clean water. Also, you will end up using more chemicals as they are also used up faster.

Some Takeaways to Remember

  • The number of gallons in your hot tub depends on its dimensions.
  • A tub's volume also depends on whether it has seats or not. The more seats in the tub, the lower the volume.
  • An 8-person tub holds more water than smaller 2 or 3-person models, regardless of its shape or style.
  • The easiest way to know how many gallons are in your hot tub is by checking your manual. The best hot tub brands will always provide a manual and make it available online for user reference.
  • You can also calculate the number of gallons in the tub manually using the dimensions or the timed fill method.

Have More Questions About Hot Tubs?

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