How Many Chlorine Tablets Do You Need in Your Pool?



Not sure how many tablets or pucks to use in your pool?

In this article, we’ll cover two approaches for figuring out the exact number of chlorine tablets to use in your pool, including an easy method and a harder but more precise method.

Quick answer: As a rough estimate, you should use one 3-inch tablet per 5,000 gallons per week, rounded up. If you want a more accurate answer, you’ll need to go through the steps outlined in this article.

The Easy Method

We’ll start with the simplest and most commonly used method for figuring out how many chlorine tablets you need to use.

Follow the steps below.

1. Get Your Pool’s Water Capacity

If you already know how much water your pool holds, you can skip ahead.

If you don’t, you’ll need to measure the length and width of your pool (or diameter for a round pool), followed by the depth. If your pool has varying levels of depth, you’ll need to measure each one.

With those measurements handy, plug them into the calculator below to get your pool volume in gallons:

2. Apply the Rule of Thumb

Now, the general rule of thumb for 3-inch tablets is to use 1 tablet for every 5,000 gallons of water your pool holds, per week.

This number is also rounded up to the nearest 5,000 increments.

For example:

  • You need 1 tablet for a 5,000-gallon pool
  • You need 2 tablets for a 9,000-gallon pool (rounded up)
  • You need 3 tablets for a 13,000-gallon pool (rounded up)
  • You need 3 tablets for a 15,000-gallon pool
  • You need 4 tablets for an 18,000-gallon pool (rounded up)

Basically, as long as you know your pool volume, you can very quickly decide how many 3-inch tablets to use by dividing that number by 5,000 and rounding up to the nearest whole number.

Alternatively, you can use our simple calculator:

Unfortunately, there’s no widely accepted rule for 1-inch chlorine tablets. This is likely because smaller pucks can dissolve considerably faster under different conditions, making them far less predictable to work with.

3. Be Ready to Make Adjustments

As with any rule of thumb, it’s probably not going to be perfect.

This method will provide you with a good estimate of where to start but you’ll need to closely monitor your chlorine level and dissolution rate (how quickly your tablets dissolve) over the coming days.

If you notice your chlorine level continues to creep up or your tablets are getting used up sooner than expected, don’t hesitate to decrease or increase the number of tablets.

The Precise Method

If you’re looking for a more scientific answer to how many chlorine tablets you need in your pool, this section is for you.

Follow the steps below.

Important: This approach assumes you’re using trichlor tablets as they are the most common type. If you’re using dichlor or calcium hypochlorite tablets, stick to the easy method above.

1. Determine Your Daily Chlorine Loss

First, you need to know how much free chlorine your pool consumes on a daily basis so you know exactly how much to put back in.

This is otherwise known as ‘chlorine demand’.

To get that number, you’ll have to test your free chlorine level at the same time every day for 3 days, then get the average by adding up the results and dividing by the number of days you tested.

Example: If you lost 1.5 ppm on day 1, 1.4 ppm on day 2, and 1. 1 ppm on day 3, your daily free chlorine loss would be 1.5 + 1.3 + 1.1 / 3 = 1.3 ppm.

Before starting the test, raise your free chlorine a little higher than usual (5-6 ppm should be enough) to allow for several days of consumption, and don’t add any additional chlorine until you’ve concluded all tests.

While you could get away with using test strips for this step, we strongly recommend using a liquid testing kit for the most accurate results.

2. Get Your Pool’s Water Capacity in Gallons

Again, if you already know your pool volume you can skip this part.

Otherwise, enter the measurements of your pool into our calculator to get your pool’s water capacity in gallons.

3. Figure Out How Long a Tablet Takes to Dissolve

The last thing you need to know is how many days it takes for a single tablet to fully dissolve in your water.

This will usually take about a week but it really depends on the conditions of your swimming pool in particular.

For example, whether you place the tablet in a floating dispenser, skimmer basket, or automatic feeder will make all the difference. The temperature of your water and pool usage is also a big factor.

Be sure to check daily and note down exactly how many days it took for the tablet or puck to crumble away.

4. Run the Numbers Through Our Calculator

At this point you should know:

  • How much free chlorine you’re losing daily (in ppm)
  • How much water is in your pool (in gallons)
  • How long a single tablet takes to dissolve (in days)

With that, you can use this calculator to get a more precise answer:

Quick disclaimer:

The calculator assumes a 3-inch tablet contributes 10 ppm of chlorine per 5,000 gallons. Most tablet manufacturers don’t provide this information but we know how much chlorine is contributed by trichlor, which most pool tablets are.

Here’s the logic we used:

  1. We know 1.5 oz trichlor in 1,000 gallons of water adds 10 ppm of chlorine (source).
  2. A chlorine tablet weighs 7.5 oz on average, so we can multiply the above weight and water volume by 5 to match.
  3. That means 7.5 oz trichlor in 5,000 gallons of water also adds 10 ppm of free chlorine.

5. Be Ready to Make Adjustments

Despite this being a more accurate approach, there will always be variables that change how different substances behave in your water.

So while it will yield the best result most of the time, changes in your water conditions will inevitably impact your chlorine demand and dissolution rate over time, forcing you to reevaluate.

Overall, if you find your free chlorine level continuously sits lower or higher than is ideal, it’s important to adjust accordingly.

So How Many Tablets Do You Need?

You could take the easy route, using 1 tablet per 5,000 gallons per week. This only involves calculating your pool volume and takes less work overall to figure out — but the result will only give you a rough starting point.

Alternatively, you can take the harder, more precise route. This involves figuring out your daily chlorine loss and tablet dissolution rate on top of your pool volume, but the result will likely be very close to reality.

Categories: Pool Care, Pool Chemistry