Pool Chlorine Calculator
Find the chlorine dose to reach a target level.
Cal-hypo ≈ 0.65, liquid ≈ 0.10-0.125
Results update as you type.
How it works
Keeping a pool safely sanitized means maintaining the right free chlorine level, and this calculator tells you how much chlorine product to add to raise it by a target amount. You enter the pool volume in gallons, the chlorine increase you want in parts per million, and the strength of your chlorine product, and it returns the amount to add in ounces and pounds plus the pure chlorine equivalent. The chemistry rests on the definition of parts per million: one ppm is one pound of chlorine per million pounds of water. Since a gallon of water weighs 8.34 pounds, the pure chlorine needed is the target ppm times the pool's water weight divided by a million. Because chlorine products are not pure, you divide by the product's available-chlorine fraction: calcium hypochlorite (cal-hypo) is around 65 to 73 percent, dichlor around 56 to 62 percent, and liquid chlorine (sodium hypochlorite) only about 10 to 12.5 percent, so you need far more liquid by weight. Regular chlorine keeps free chlorine in the recommended 1 to 3 ppm range, while shocking raises it much higher temporarily to kill algae and contaminants. Always add chlorine as directed, with the pump running, and retest before swimming. Enter your pool volume, target increase, and product strength to find the dose.
Pure lb = (ppm × gallons × 8.34) ÷ 1,000,000; product = pure ÷ strength
One ppm means one part per million by weight, so the pure chlorine needed equals the target ppm times the pool's water weight (gallons times 8.34 pounds) divided by one million. Dividing by the product's available-chlorine fraction converts that to the actual weight of product to add.
Source:Pool chemistry (parts per million)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter pool volume and chlorine increase wanted.
- 2
Adjust the options
Adjust product strength if they apply — sensible defaults are already set.
- 3
Read your result
Product to add updates instantly as you type — no button to press.
Frequently asked questions
How much chlorine do I add to my pool?
Multiply the target ppm increase by your pool's water weight (gallons times 8.34) and divide by a million to get pure chlorine, then divide by your product's strength. To raise 10,000 gallons by 5 ppm with 65 percent cal-hypo, add about 10 ounces. The calculator handles the math for any volume, target, and product.
What chlorine level should a pool have?
Free chlorine should stay in the range of 1 to 3 parts per million for safe, sanitized water, with 2 to 3 ppm a common target. Shocking temporarily raises it much higher, often to 10 ppm or more, to kill algae and break down contaminants. Always let levels return to the safe range before swimming.
Why does product strength matter so much?
Chlorine products vary widely in available chlorine. Calcium hypochlorite is about 65 to 73 percent, dichlor 56 to 62 percent, and liquid chlorine only 10 to 12.5 percent. Because liquid is so dilute, you need several times more of it by weight than cal-hypo for the same effect. Using the correct strength ensures you add the right amount.
What is the difference between chlorinating and shocking?
Regular chlorination maintains free chlorine in the 1 to 3 ppm range for day-to-day sanitizing. Shocking adds a large dose to spike chlorine well above normal, quickly killing algae, bacteria, and breaking down chloramines that cause odor and irritation. Shock periodically or after heavy use, rain, or algae blooms, then wait for levels to drop before swimming.
How should I add chlorine safely?
Add chlorine with the pump running so it circulates, following the product's instructions, and never mix different chlorine products together. Granular products are often pre-dissolved or broadcast over the surface, while liquid is poured around the pool. Add in the evening to reduce sunlight loss, keep products stored safely, and always retest the water before anyone swims.