Pool Chlorine Calculator
Pool Chlorine Calculator
Work out how much chlorine to add to a pool or hot tub to raise the free chlorine from what you tested to where you want it, for liquid chlorine, bleach, cal hypo, dichlor or trichlor, with the stabilizer and calcium each one adds and the chlorine level your stabilizer calls for.
Free chlorine now and after
Chlorine needed against stabilizer
One ppm is one milligram of available chlorine per liter, so raising 10,000 US gallons (37,854 liters) by 1 ppm takes 37.9 grams of available chlorine. Liquid chlorine is sold by trade percent, grams per 100 mL; bleach strength is by weight and is converted with a typical density. Cal hypo, dichlor and trichlor strengths are percent available chlorine by weight. Dichlor adds about 0.9 ppm of stabilizer and trichlor about 0.6 ppm for each 1 ppm of chlorine; cal hypo adds about 0.7 ppm of calcium hardness. The CDC recommends free chlorine of at least 1 ppm in pools and 3 ppm in hot tubs, at least 2 ppm in pools with stabilizer, and pH 7.0 to 7.8. The minimum of 7.5 percent of the stabilizer and the shock level of 40 percent are common pool care rules, not code. Always follow the product label. The CSV, image and printed report contain the values you entered, nothing preloaded.
How to use this tool
Enter the pool or hot tub volume, pick the chlorine product you have, and type the free chlorine you just tested and the level you want. Add the stabilizer (CYA) reading if you have one. The amount to add appears at the top, with what else the product puts in the water and the chlorine level your stabilizer calls for.
The gauge shows where the water is now against the band from the minimum to the shock level, and the second chart shows how that band rises with stabilizer. The table gives the dose for 1 ppm for every product, useful when you switch.
How the dose is worked out
A ppm of chlorine is one milligram per liter. Raising 10,000 US gallons, which is 37,854 liters, by 1 ppm takes 37.9 grams of available chlorine. The page multiplies the raise you want by the volume in liters to get grams of chlorine, then divides by the product’s strength.
Liquid chlorine is sold by trade percent, grams of available chlorine per 100 mL, so 12.5 percent holds 125 grams per liter. Bleach labels give percent by weight, which the page converts with a typical density. Dry products are percent available chlorine by weight: 65 percent cal hypo gives 0.65 g of chlorine per gram.
Dose for 1 ppm by product
| Product | 1 ppm, 10,000 gal | 1 ppm, 10,000 L | Also adds per 1 ppm |
|---|---|---|---|
| Liquid chlorine 12.5% | 10.2 fl oz | 80 mL | nothing else |
| Liquid chlorine 10% | 12.8 fl oz | 100 mL | nothing else |
| Bleach 8.25% | 14.7 fl oz | 115 mL | nothing else |
| Bleach 6% | 20.7 fl oz | 162 mL | nothing else |
| Cal hypo 65% | 2.05 oz | 15 g | 0.7 ppm hardness |
| Cal hypo 73% | 1.83 oz | 14 g | 0.7 ppm hardness |
| Dichlor 56% | 2.38 oz | 18 g | 0.9 ppm CYA |
| Dichlor 62% | 2.15 oz | 16 g | 0.9 ppm CYA |
| Trichlor 90% | 1.48 oz | 11 g | 0.6 ppm CYA |
Multiply by the ppm raise and by your volume over 10,000. Liquid chlorine strengths are trade percent; bleach is converted from percent by weight.
A worked example you can check on paper
A 15,000 gallon pool tests at 1 ppm free chlorine and 30 ppm of stabilizer, and the target is 3 ppm. The raise is 2 ppm, and 15,000 gallons is 56,781 liters, so the pool needs 2 times 56,781, about 114 grams of available chlorine. At 125 grams per liter, 12.5 percent liquid chlorine takes 0.908 liters, 30.7 fl oz, just under a quart.
With 30 ppm of stabilizer the minimum is 7.5 percent of 30, 2.25 ppm, so 3 ppm is comfortably above it. Using dichlor instead would take 7.2 oz and add about 1.8 ppm of stabilizer.
Mistakes that catch people out
Guessing the volume. A pool 20 percent bigger than you think gets 20 percent too little. Work it out once with the Pool Volume Calculator.
Using old liquid chlorine. It loses strength in storage, faster in heat. A jug that has sat through summer may be well below the label.
Letting stabilizer creep up. Tabs and dichlor add CYA with every dose, and the only way out is draining. Test CYA monthly.
Mixing chemicals. Never pre mix products, never put chlorine and acid in the same bucket, and keep cal hypo away from trichlor: the combination can ignite.
Popular calculations
Each opens the calculator with its own address, and every value can be changed once it is open.
By pool size, 12.5% liquid chlorine
Other products
Shocking
New water and above ground pools
Hot tubs
Metric
How this was checked
The engine was tested in Node against hand calculations: 1 ppm in 10,000 gallons is 37.85 grams of available chlorine, which is 10.24 fl oz of 12.5 percent liquid chlorine, 2.05 oz of 65 percent cal hypo and 1.48 oz of 90 percent trichlor, matching the figures on common pool dosing charts. Stabilizer and calcium additions were checked from the chemistry of dichlor, trichlor and calcium hypochlorite, and liter inputs were checked by converting by hand.
Every address in the lists above was then opened and checked for a distinct title, the right answer, charts that render, and clean CSV, image and print output containing only that calculation, at desktop, tablet and phone widths.
Common questions
How much liquid chlorine do I add to raise my pool 1 ppm?
About 10.2 fl oz of 12.5 percent liquid chlorine, or 12.8 fl oz of 10 percent, per 10,000 gallons. A 15,000 gallon pool going from 1 to 3 ppm takes about 30.7 fl oz of 12.5 percent, roughly a quart.
How much bleach do I put in my pool?
Household bleach is weaker than pool chlorine: about 20.7 fl oz of 6 percent or 14.7 fl oz of 8.25 percent bleach raises 10,000 gallons by 1 ppm. Use plain, unscented bleach without thickeners or additives.
What should free chlorine be in a pool?
The CDC recommends at least 1 ppm in pools, at least 2 ppm when the pool uses stabilizer, and at least 3 ppm in hot tubs, with pH 7.0 to 7.8. Many owners keep 2 to 4 ppm, and more when stabilizer is high.
Why does stabilizer change how much chlorine I need?
Cyanuric acid protects chlorine from sunlight but binds part of it, making it slower to act. A common rule keeps free chlorine at least 7.5 percent of the CYA level, so a pool at 60 ppm of CYA needs about 4.5 ppm to do the same job as 2 ppm at low CYA.
How much shock does my pool need?
Shocking means raising free chlorine to a high level and holding it until the water clears. A common target is about 40 percent of the CYA level, around 12 ppm at 30 ppm of CYA. For 15,000 gallons from 1 ppm, that is about 1.3 gallons of 12.5 percent liquid chlorine.
Should I use trichlor or dichlor all season?
They are convenient, but each 1 ppm of chlorine from dichlor adds about 0.9 ppm of CYA and from trichlor about 0.6 ppm. Over a season that builds up, so many owners switch to liquid chlorine or cal hypo once CYA reaches about 30 to 50 ppm.
Related Calculators and Reference
- Pool Volume Calculator: gallons and liters for any pool shape.
- Volume Converter: gallons, liters and cubic meters.
- Water Heater Size Calculator: tank and tankless sizes for a home.
- Temperature Converter: water temperature in °F and °C.
- PPM to mg/L Converter: test kits report chlorine in ppm, and this shows why that matches mg/L in pool water.
- CDC: Home Pool and Hot Tub Water Treatment and Testing: recommended chlorine and pH levels.