Pool Chlorine Calculator
This pool chlorine calculator works out how much chlorine to add to raise your free chlorine (FC) from its current reading to the level you want. Enter your pool volume in gallons or liters, your current and target FC in ppm, and the product you use: liquid chlorine, cal-hypo, dichlor or trichlor.
It converts the ppm increase into pounds of pure chlorine, then divides by your product's strength to give a dose you can measure: fluid ounces or gallons of liquid, or ounces and pounds of granules, with metric equivalents. It also flags the stabilizer or calcium that some products add, since those build up in the water over a season.
Pool Chlorine Calculator
How to Use the Pool Chlorine Calculator
- 1
Enter your pool volume
Type the volume and choose US gallons or liters. If you do not know it, work it out first with a pool volume calculator.
- 2
Enter current and target free chlorine
Use a fresh test reading for current FC in ppm, and set the target. The default target is 3 ppm.
- 3
Choose your product
Pick liquid chlorine, cal-hypo, dichlor or trichlor. The strength fills in automatically, and you can change it to match your label.
- 4
Measure and add the dose
The result shows how much product to add, the pounds of pure chlorine behind it, and any CYA or calcium it adds. Add it as the label directs and retest once the water has circulated.
How the chlorine dose is calculated
One ppm means one pound of chlorine per million pounds of water. A US gallon of water weighs 8.34 pounds, so the pounds of pure chlorine you need is the ppm increase times the gallons times 8.34, divided by one million.
No product is pure chlorine, so that figure is divided by the product's available chlorine. For dry products, that gives pounds of product directly. For liquid chlorine the strength is treated as trade percent, meaning weight of chlorine per volume, so one gallon of 12.5% liquid carries 0.125 x 8.34 = 1.04 pounds of chlorine.
Pure chlorine (lb) = ppm increase x pool gallons x 8.34 / 1,000,000; dry product (lb) = pure lb / strength; liquid (gal) = pure lb / (strength x 8.34)Worked example: 15,000 gallons from 1 to 3 ppm
Your pool holds 15,000 gallons, your test shows 1 ppm free chlorine, and you want 3 ppm.
- Increase needed: 3 - 1 = 2 ppm
- Pure chlorine: 2 x 15,000 x 8.34 / 1,000,000 = 0.2502 lb
- With 12.5% liquid chlorine: 0.2502 / (0.125 x 8.34) = 0.24 gallons, or about 30.7 fl oz (908 mL)
- With 65% cal-hypo instead: 0.2502 / 0.65 = 0.38 lb, or about 6.2 oz by weight (175 g), which also adds about 1.4 ppm of calcium hardness
- A metric version: a 50,000 liter pool raised from 1 to 3 ppm needs about 800 mL of 12.5% liquid chlorine.
Amount to raise 10,000 gallons by 1 ppm
Use this as a quick check. Multiply by the ppm increase and by your volume divided by 10,000. The last column shows what else the product adds for each 1 ppm of chlorine.
| Product | US amount | Metric amount | Also adds per 1 ppm FC |
|---|---|---|---|
| Liquid chlorine 10% | 12.8 fl oz | 379 mL | Salt only |
| Liquid chlorine 12.5% | 10.2 fl oz | 303 mL | Salt only |
| Cal-hypo 65% | 2.1 oz (weight) | 58 g | About 0.7 ppm calcium |
| Cal-hypo 73% | 1.8 oz (weight) | 52 g | About 0.7 ppm calcium |
| Dichlor 56% | 2.4 oz (weight) | 68 g | About 0.9 ppm CYA |
| Trichlor 90% | 1.5 oz (weight) | 42 g | About 0.6 ppm CYA |
Choosing a target and a product
The CDC recommends keeping free chlorine at 1 ppm or more in pools and 3 ppm or more in hot tubs, and many owners aim for about 3 ppm in a pool. The chlorine level you actually need rises with your cyanuric acid (stabilizer) level, because CYA holds some chlorine in reserve. That is also why shock levels are set from your CYA reading rather than a single number.
Liquid chlorine adds nothing but salt, which makes it easy to use every day. Cal-hypo raises calcium hardness. Dichlor and trichlor are stabilized, so they raise CYA with every dose. They are handy for outdoor pools early in the season but can push CYA too high if they are your only chlorine source.
Tips and common mistakes
- Test before you dose. An old reading can lead to a double dose.
- Liquid chlorine loses strength over time, especially in heat. Old liquid may raise FC less than calculated, so retest and top up rather than adding more up front.
- Plain unscented household bleach works like liquid chlorine. Enter its label percentage in the strength box, and avoid scented, splash-less or thickened bleach.
- Add chlorine in the evening when possible. Sunlight breaks down unstabilized chlorine quickly.
- Pour liquid chlorine slowly in front of a return jet with the pump running so it mixes well.
Chemical safety
Your product label and local health rules come first. Store chlorine products apart from each other and from acids, in a cool, dry, ventilated place. Never mix different chlorine products, never mix chlorine with acid, and always add chemicals to water, not water to chemicals. Wear gloves and eye protection, keep children and pets away while dosing, and keep swimmers out until the level is back in the normal range.
Features
- Raise free chlorine from your current reading to any target ppm
- Liquid chlorine (10% or 12.5%), cal-hypo (65% or 73%), dichlor (56%) and trichlor (90%)
- Editable product strength to match your label
- Liquid doses in fluid ounces, gallons, mL or liters; dry doses in ounces, pounds, grams or kg
- Pool volume in US gallons or liters, with a note on the CYA or calcium each dose adds
Frequently Asked Questions
How much liquid chlorine do I add to raise 1 ppm?
For 10,000 gallons, about 10.2 fl oz of 12.5% liquid chlorine or 12.8 fl oz of 10% raises free chlorine by 1 ppm. Scale by your volume and the increase you need. A 15,000 gallon pool going from 1 to 3 ppm needs about 30.7 fl oz of 12.5% liquid chlorine.
How much chlorine do I need to shock my pool?
Shock is just a high chlorine dose, and the right level depends on your cyanuric acid reading. Once you know your target, enter it here. For example, raising a 20,000 gallon pool from 0.5 to 10 ppm takes about 194.6 fl oz, or 1.52 gallons, of 12.5% liquid chlorine. Keep swimmers out until chlorine drops back to normal.
What should my free chlorine level be?
The CDC recommends at least 1 ppm of free chlorine in pools and at least 3 ppm in hot tubs and spas. Many pool owners keep about 3 ppm. If your water has a lot of cyanuric acid (stabilizer), you need more free chlorine for the same sanitizing effect, so check your CYA level too.
How much cal-hypo shock do I need for 10,000 gallons?
At 65% strength, about 2.1 ounces by weight of cal-hypo raises 10,000 gallons by 1 ppm, and 73% cal-hypo takes about 1.8 ounces. Raising 10,000 gallons by 10 ppm with 65% cal-hypo therefore takes about 1.28 pounds. Each 1 ppm of chlorine from cal-hypo also adds roughly 0.7 ppm of calcium hardness.
Can I use household bleach in my pool?
Plain, unscented household bleach is sodium hypochlorite, the same chemical as pool liquid chlorine, only weaker. Enter the percentage from the label in the strength box. Avoid scented, splash-less or gel bleach, which contain additives. Because bleach is weaker, you need more of it than 10% or 12.5% pool chlorine for the same increase.
Can I mix different chlorine products together?
No. Mixing chlorine products, for example cal-hypo with trichlor, can cause a violent reaction, fire or toxic gas. Add each chemical separately to the pool water with the pump running, wait for it to circulate before adding anything else, and never combine chlorine with acid. Follow the label on every product.
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