How Much Chlorine to Add to a Pool? (Per Gallon of Water)



Are you looking to add chlorine to your swimming pool but not quite sure how much to use?

This article will guide you through the exact steps for measuring out the correct dose of chlorine for your pool, whether you’re using chlorine tablets, granular chlorine or even liquid chlorine.

Why You Can’t Just Add Chlorine on a Schedule

It would be convenient if you could add a set amount of chlorine to your pool every X number of days and be done with it.

Unfortunately, this isn’t a realistic solution because chlorine isn’t consumed at a constant rate.

Factors such as bather load, sun exposure, and other chemical levels in your pool all dictate not only how effective your chlorine is, but also how quickly your chlorine is used up.

Ultimately, this is why you must test your water before adding new chlorine, or else you risk adding too little or too much.

Note: Chlorine tablets can be used somewhat predictably to maintain your chlorine level over time, however this does not free you from regular chlorine testing and correction. We’ll talk more about this later in the article.

What You Need to Know Before Adding Chlorine

The right amount of chlorine to add to your pool water largely depends on three pieces of information.

Let’s break it down:

1. Your Pool’s Capacity in Gallons

This is just how much water your pool holds, and it’s a number you’ll be coming back to often throughout your pool care journey.

For this, you’ll need to measure the width and length of your pool – or diameter, if you have a round pool. You’ll also need to measure the depth of your pool in both the shallowest and deepest areas.

Once you have these numbers, simply plug them into a calculator like this one to get your pool capacity in gallons.

2. Your Current Chlorine Level

Before you can figure out how much chlorine to add to your pool, you first need to know how much sanitizer is already in the water.

In particular, you need to know the free chlorine level.

You can use either a test strip or a liquid test kit for this part, though it’s always worth investing in a liquid test kit for the most accurate results.

The exact steps for testing your water will depend on the type and brand of test kit you’re using.

While you could follow our general directions on using strips or liquid kits for testing your chlorine level, it’s always best to follow the manufacturer’s instructions for the particular product you have.

3. Your Target Chlorine Level

Typically, a pool’s free chlorine level should sit between 1 and 3 parts per million (ppm) in order to remain sanitary enough for swimming.

However, some swimming pools will consume more than this, especially if the pool sees a lot of use or if environmental factors introduce more contamination into the water.

This is why some pool owners prefer to keep their free chlorine level between 3 and 5 ppm, which is still perfectly safe for swimming.

If you’re not sure what chlorine level to choose, we recommend aiming for 2-3 ppm and adjusting from there if necessary.

You should know: Chlorine stabilizer (cyanuric acid) reduces the effectiveness of your chlorine, meaning you’ll need to add even more chlorine than usual if your stabilizer level is particularly high.

How to Calculate How Much Chlorine to Add to Your Pool

Now that you have the above information, it’s time to figure out exactly how much chlorine your pool needs.

Since different types of chlorine come in various strengths and physical forms, it may require vastly different amounts to raise the chlorine level by the same degree.

Most chlorine packaging will tell you how much to use to raise your water by 1 ppm per 10,000 gallons, but here’s pretty much what you can expect:

Type of granular chlorineTo raise 1 ppm per 10,000 gallons
Dichlor (55-62%)2.4 oz by weight
Trichlor (90%)1.5 oz by weight
Cal-hypo (48%)2.8 oz by weight
Cal-hypo (53%)2.5 oz by weight
Cal-hypo (65%)2.1 oz by weight
Cal-hypo (73%)1.8 oz by weight
Lithium hypo (28-35%)3.8 oz by weight

Of course, this still requires some cumbersome math if you’re not fortunate enough to be working with round numbers (unlikely at best).

No stress, we plugged this data into our handy chlorine dosage calculator:

See? Easy.

What If You’re Using Chlorine Tablets?

Most chlorine tablets are trichlor, which is 90% available chlorine.

With that being said, the rules are a little different for tablets because they’re a pre-defined size and they’re also slow-dissolving.

As a result, where you can quickly increase the sanitizer level using a specific dosage of granular or liquid chlorine, chlorine tablets are far better at maintaining your chlorine level on autopilot.

As a general rule, a single 3-inch tablet should cover you for 5,000 gallons of water, and you should always round up.

For example:

  • For a 10,000-gallon pool, you would use 2 tablets.
  • For a 15,000-gallon pool, you would use 3 tablets.
  • For an 18,000-gallon pool, you would use 4 tablets.

You should know: Trichlor tablets contain cyanuric acid (CYA). Regularly dissolving this type of chlorine in your pool will lead to a high CYA level, which can only be fixed through draining and refilling.

How Often Should You Add Chlorine?

Similar to the question of how much, how often also largely depends on the type of chlorine you’re using in your pool.

Granular and liquid chlorine is dissolved quickly in a pool, meaning they get to work within minutes of being added to your water. This allows you to quickly spike your chlorine to the necessary level, but it’s all downhill from there.

As a result, for these types of chlorine, you will need to test and top up your chlorine at least 2-3 times per week, and potentially as often as every day during heavy pool use.

Chlorine tablets, on the other hand, dissolve slowly over time. While they won’t provide a sudden spike of chlorine in your pool, they do provide a more hands-off approach to maintaining your sanitizer level.

Tablets typically last up to a week in your pool, and it’s important to check your dispenser at least that often to ensure tablets are being replaced as soon as they’re used.

Conclusion: Let the Numbers Guide You

Adding the right amount of chlorine to your pool is essential for proper sanitation as well as a comfortable swim.

Whether you settle on 3 ppm or 5 ppm as your target chlorine level, your pool capacity and current chlorine level should always be the starting point when figuring out the correct chlorine dosage.

Simply stick to a regular water testing schedule and let the numbers guide you on what to do next.

Categories: Pool Care, Pool Chemistry