Pool Borate Calculator: How Much Borax Do You Need?

Borates are a common chemical that many swimming pool owners add to their pool water to act as a pH buffer and protect against algae. It’s not a typical part of your usual water chemistry (there’s likely zero borax in your pool water today if you haven’t intentionally added any), but can be helpful. There are pros and cons of using borax though, so make sure to read my guide on using borax in your pool (if you haven’t already) to understand it completely.

Below, you’ll find all the steps you need to calculate how much borax to add to your pool water, and on the flip side, how much pool water to replace if your borax levels are too high. Let’s get started.

Here are all the steps you need to follow:

Test Your Borate Level

The first step is to test the current borate level in your swimming pool. You can use simple borate test strips to find that out. I recommend keeping your borate level around 30-500 ppm (parts per million).

Calculate The Volume of Your Pool

The next step is to calculate the volume of your pool (if you don’t know that number already). You can use my calculator below to figure out the approximate number of gallons.


Got that number? Let’s move on.

Time to Calculate For Borax

Okay, now it’s time to calculate what to add or remove to balance your borax levels. Depending on the borax test results from earlier, you’ll do one of two things:

If your borax level is below the desired range, you want to add borax or boric acid to your pool water. You can use the selector in the calculator below to specify your choice. You can also add it by weight (measured in ounces) or volume (ounces by volume), so make sure to select your measurement below as well.

If your borax level is above the desired range, you need to replace a percentage of pool water with fresh water to dial back the borates. If that’s the case, my calculator below will spit out a whole number (something like “37.6”), which represents the percentage of water you need to replace. So, in that example, you need to replace 37.6% of the current pool water with fresh water.

Make sense? Let’s get to calculating.


Let me know if you’re still confused or have further questions. I’m always here to help! Pool chemistry can feel complicated sometimes, so make sure to check out my swimming pool chemicals guide for more information.

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