Pool chlorine calculator
Enter your pool's volume, your free chlorine reading and the level you want. Choose the product you have. You'll get the dose, the side effects on stabilizer, calcium or salt, and a suggested chlorine level for your stabilizer reading.
Don't know your volume? Use the pool volume calculator. Bringing the pool up to shock level? Use the shock calculator.
How much chlorine does a pool need?
The US Centers for Disease Control and Prevention (CDC) recommends at least 1 ppm free chlorine in pools, and at least 2 ppm in pools that use cyanuric acid (stabilizer) or stabilized chlorine such as dichlor and trichlor. In practice, the right level depends on how much stabilizer is in the water, because stabilizer holds most of the chlorine in reserve. The higher the CYA, the more free chlorine you need for the same sanitizing power.
A guideline widely used by pool owners, popularized by the Trouble Free Pool community, keeps free chlorine at about 7.5% of the CYA level or more (about 5% with a salt chlorine generator, which adds chlorine steadily all day). At 40 ppm CYA that's a minimum of 3 ppm. Our chlorine and stabilizer guide explains why, with a full table.
The formula
Liquid: milliliters = grams ÷ (strength % ÷ 100)
Granular: grams of product = grams ÷ (available chlorine % ÷ 100)
One ppm is one milligram per liter. A 10,000-gallon pool holds 37,854 liters, so 1 ppm of chlorine there is 37.9 grams. Liquid chlorine strength is sold as "trade percent", grams of available chlorine per 100 mL, so 12.5% liquid has 0.125 g per mL. Granular products list "available chlorine" as a percentage by weight on the label.
How much raises 10,000 gallons by 1 ppm
| Product | Amount per 1 ppm in 10,000 gal | What else it adds (per 1 ppm of chlorine) |
|---|---|---|
| Liquid chlorine 12.5% | 10.2 fl oz | About 1.65 ppm salt |
| Liquid chlorine 10% | 12.8 fl oz | About 1.65 ppm salt |
| Bleach 8.25% | 15.5 fl oz | About 1.65 ppm salt |
| Bleach 6% | 21.3 fl oz | About 1.65 ppm salt |
| Cal-hypo 65% | 2.1 oz (weight) | About 0.7 ppm calcium hardness |
| Cal-hypo 73% | 1.8 oz | About 0.7 ppm calcium hardness |
| Dichlor 56% | 2.4 oz | About 0.9 ppm CYA |
| Trichlor 90% | 1.5 oz | About 0.6 ppm CYA, and lowers pH and alkalinity |
The side effects come from the chemistry of each product. Dichlor and trichlor are cyanuric acid molecules carrying chlorine, so every dose leaves stabilizer behind. Cal-hypo is calcium hypochlorite and leaves calcium. Liquid chlorine and bleach are sodium hypochlorite and leave a little salt, which is harmless at these amounts. Use plain, unscented bleach without thickeners or "splash-less" additives.
Worked example
A 15,000-gallon pool reads 1 ppm free chlorine, and you want 4 ppm: an increase of 3 ppm. 3 × 15,000 × 3.785 ÷ 1,000 ≈ 170 g of chlorine.
- With 12.5% liquid chlorine: 170 ÷ 0.125 ≈ 1,363 mL, or about 46 fl oz.
- With 6% bleach: 170 ÷ 0.06 ≈ 2,839 mL, or about 96 fl oz, three-quarters of a gallon.
- With 65% cal-hypo: 170 ÷ 0.65 ≈ 262 g, or about 9.2 oz. It also adds about 2 ppm calcium.
- With dichlor: about 10.7 oz, which also adds about 2.7 ppm CYA.
Choosing a chlorine product
- Liquid chlorine or bleach adds nothing that builds up except a little salt, so it's the easiest to manage long-term. It does lose strength in storage, faster when warm, so buy it fresh and keep it cool and shaded.
- Trichlor tablets are convenient in a floater or feeder, but they keep adding CYA and they're acidic. Over a season, CYA can climb high enough that you need much more chlorine, or a partial drain.
- Dichlor dissolves quickly and is nearly pH-neutral. It's useful for starting up a pool with no stabilizer, but like trichlor it keeps adding CYA.
- Cal-hypo adds calcium, which is fine if your water is soft and a problem if it's already hard.
Frequently asked questions
Why does my chlorine disappear overnight?
Chlorine is used up by sunlight, swimmers, debris and algae. With low or no stabilizer, sunlight alone can destroy most of it in a few hours. If chlorine drops a lot overnight, when there's no sun, something in the water is using it up, often the start of algae. Our shock guide covers the overnight chlorine loss test.
Free chlorine, total chlorine, combined chlorine: which one goes here?
Use free chlorine (FC), the chlorine available to sanitize. Total chlorine includes combined chlorine (chloramines), which has already reacted. Combined chlorine = total − free. If it's above about 0.5 ppm, the pool needs extra chlorine to clear it.
Can I use household bleach in my pool?
Yes, as long as it's plain, unscented bleach with nothing else added. It's the same chemical as pool liquid chlorine, just weaker. Check the strength on the label, since it varies by brand and drops as the bottle ages.