Pool chlorine calculator
Enter the pool volume (or its size), the free chlorine you measured and the level you want. The calculator gives the dose of liquid chlorine, cal-hypo, dichlor or trichlor for the strength printed on your product.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose the units and how you know the volume: type it in, or enter the size of a rectangular or round pool.
- Enter the free chlorine you measured with a test kit and the level you want.
- Pick your product and check its strength against the label.
- Add the amount shown, spread around the pool with the pump running, and retest later.
How it works
1 ppm of chlorine in water is 1 mg per litre, so the chlorine to add is:
available chlorine (g) = (target − current) × volume (L) ÷ 1000
The product amount is that chlorine divided by its strength: grams for granules and tablets (strength by weight), millilitres for liquid (trade percent, grams per 100 mL). A rectangular pool holds length × width × average depth; a round one π ÷ 4 × diameter² × depth.
Example
A 15,000-gallon pool reads 1 ppm and you want 3 ppm. The rise is 2 ppm. The product volume is 15,000 × 128 fl oz × 2 ÷ 1,000,000 ÷ 0.125 = 30.7 fl oz of 12.5% liquid chlorine (0.24 gal). That carries 4 oz of available chlorine. With 65% cal-hypo the same rise needs 6.2 oz of granules.
Tips and common mistakes
- Measure free chlorine, not total chlorine, and test again after the water has circulated.
- Liquid chlorine loses strength in storage, especially when warm, so an old jug may need more than the calculation shows.
- Never mix different chlorine products, or chlorine with acid, in a bucket. Add them to the pool separately.
- A volume estimate that is 20% off makes the dose 20% off. If you are unsure of the volume, the water volume calculator works it out from the shape.
Frequently asked questions
How much liquid chlorine raises a pool by 1 ppm?
1 ppm is 1 mg per litre. In 10,000 US gallons (37,854 L) that is about 37.9 g of available chlorine, or 10.2 fl oz of 12.5% liquid chlorine. Double the volume or the ppm and the dose doubles.
What strength should I enter?
The number on your product. Liquid pool chlorine is often sold as 10% or 12.5% (trade percent: grams of available chlorine per 100 mL). Granular cal-hypo is commonly 65–73%, dichlor about 56% and trichlor about 90% available chlorine. The defaults are only typical values.
Why does the calculator show a CYA or calcium rise?
Stabilised chlorine adds cyanuric acid with every dose: about 0.9 ppm CYA per 1 ppm of chlorine from dichlor and 0.6 ppm from trichlor. Cal-hypo adds about 0.7 ppm of calcium hardness per 1 ppm of chlorine. These follow from the chemical formulas, and they build up over a season.
Can I use household bleach?
Plain unscented bleach is sodium hypochlorite, the same chemical as liquid pool chlorine, but usually weaker. Bottles often give the percentage of sodium hypochlorite by weight, which is not exactly the trade percent, so treat the result as approximate and test the water afterwards.
What free chlorine level should I aim for?
Follow your local pool rules and the product label. A range of about 1–3 ppm is often quoted for home pools, and the right level also depends on the cyanuric acid level. Always retest after the chlorine has mixed.