Hot tubs can be found in all shapes and sizes, and this can make calculating how much water a hot tub holds a bit of a challenge.

Luckily, there are a few standard hot tub sizes and some quick ways to calculate about how much water any particular tub will hold.

Learning about how often to change the water or add more to the hot tub can also keep your tub clean and working perfectly.

## How much water does a hot tub hold?

Hot tubs are generally found in three standard sizes.

Small hot tubs, which are meant to hold between two and four people, are between five and seven feet long and usually measure between 29 and 35 inches tall.

Medium-sized hot tubs, which hold between five and six people, are between six and a half and seven and a half feet long and measure 33 to 38.5 inches high.

Large hot tubs, which are meant for seven or more people, are between seven and nine feet long and measure between three feet and 38 inches tall.

**Medium hot tubs, in general, hold anywhere from 320 to 475 gallons of water. Small hot tubs hold a little bit less and can range from 145 to 245 gallons of water. Large hot tubs, on the other hand, can easily hold 450 to 500 gallons of water or more.**

## How can I measure the volume of my hot tub?

It’s not too difficult to get a good estimate for how much water your hot tub will hold by using a simple calculation. For square or rectangular hot tubs, first measure the width, length, and depth of the inside of the tub in inches, not feet.

Then multiply the depth and width and multiply again by the length. Divide the resulting number by 1,728. If the hot tub has seats, multiply the resulting number by 2.4. If the hot tub doesn’t have seats, multiply the number by 4.8 instead.

If your hot tub is round or has more than four sides, measure the diameter of the tub, again in inches instead of feet, and multiply the diameter times the diameter again, times the depth, and then divide the resulting number by 1,728. Multiply by either 2.4 or 4.8, depending on whether or not the tub has seats.

If your hot tub is an uneven shape, there may be some slight fluctuations in just how many gallons the tub will hold, but the above calculation will get you very close to an accurate answer. Not only will this calculation help when it comes to filling the tub or adding water, but it can also help you determine what amounts of chemicals to add to the hot tub to ensure that it stays clean.

You can also determine how many gallons of water a hot tub holds by using fill time to get a good estimate. Time how long it takes to fill the tub, and then convert the minutes to seconds. Write down the total number of seconds.

Using the same hose with which you filled the hot tub, time how long it takes to fill a one-gallon bucket or container. Next, divide the number of seconds it took to fill your hot tub by the number of seconds it took to fill the gallon container. The final number should give you a relatively accurate number of gallons.

## How often should I change the water?

Chemicals or other additives can help your hot tub stay clean, clear, and bacteria-free. However, the warm water and small space mean that bacteria can still grow easily, so it’s a good idea to completely change the water in your hot tub periodically.

Changing the water now and then also helps to prevent mineral buildup along the sides of the tub and helps to keep the water much clearer.

**In general, emptying and completely refilling the hot tub every three months is a good schedule to maintain.**

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For a more exact schedule concerning how often to change your water, however, you can use the size of your hot tub to calculate.

Take the hot tub’s volume and divide it by three, and then divide the resulting number by the number of people who usually use the hot tub on a daily basis. The answer will give you a number of days.

For example, if your answer is 30, you should completely change the water once a month or so.

If you find that your hot tub water has a strange odor, if the tub develops a foam that can’t be treated, or if the water becomes cloudy and can’t be treated using a shock treatment, you may need to change the water sooner than planned.

These issues are usually caused by water buildup or bacteria, and emptying the tub is sometimes the only way to solve the problem.

You may also need to change the water more or less frequently depending on other factors. For example, if the hot tub is outside, you might need to change the water more frequently.

## How often should I add water?

How often you’ll need to add water to your hot tub depends on a few factors. If your hot tub is outside or in a warm area, the water will evaporate more quickly. In addition, if you splash water out, you’ll need to add water more often. Luckily, adding water to the hot tub is quite simple. You can easily put a hose into the tub and fill until the tub is at the correct level.

After filling the hot tub, you may need to test your chemical levels a few days later in order to ensure that everything is balanced. Keeping your hot tub full will also help you when it comes to adding the correct amount of chemicals every time.