How much chlorine does your pool need?
Enter the pool and the product, get the amount to raise free chlorine to your target.
Don't know the gallons? Use the pool volume calculator.
Label examples: liquid chlorine 12.5% sodium hypochlorite; calcium hypochlorite 65% available chlorine (on a 68% product); dichlor 56% (62% anhydrous); trichlor 90%. Type your own label's number.
How much chlorine do I add to my pool?
Chlorine in water is measured in ppm, which is 1 milligram per liter, so raising a pool by 1 ppm takes 1 mg of chlorine (as Cl2) for every liter. A 10,000-gallon pool holds 37,854 liters, so each ppm takes 37.85 g (1.34 oz) of chlorine. Divide by the share of the product that is available chlorine: trichlor at 90% needs 42.06 g (1.48 oz) per ppm, and calcium hypochlorite at 65% needs 58.2 g (2.05 oz). An EPA-registered label for a 68% calcium hypochlorite (minimum 65% available chlorine) says 20 ounces per 10,000 gallons gives 10 ppm, and the math gives 20.5.
What free chlorine level does the CDC recommend?
At least 1 ppm in a pool, at least 2 ppm if the pool uses cyanuric acid, and at least 3 ppm in a hot tub, with pH 7.0 to 7.8. The 2024 Model Aquatic Health Code (clauses 5.7.3.1.1.2.1 to 5.7.3.1.1.2.3) sets the same minimums for public pools; its maximum is whatever the product label allows, and it treats more than 10 ppm with swimmers in the water as an imminent health hazard (6.6.3.1A). For a fecal incident it calls for 2 ppm held for 25 minutes after a formed stool and 20 ppm held for 12.75 hours after diarrhea, using only non-stabilized chlorine (6.5). For ordinary shocking, follow the dose on your product label.
Is 12.5% liquid chlorine 12.5% of what?
Jugs state strength in different ways, and the difference is large because bleach is denser than water. A label of 12.5% sodium hypochlorite by weight is 11.9% available chlorine by weight, about 143 grams of chlorine per liter; “trade percent” means grams of chlorine per 100 milliliters, so 12.5% trade is 125 grams per liter. In a 10,000-gallon pool, 1 ppm takes 9.0 fluid ounces of the first and 10.2 fl oz of the second. Choose the basis your label uses in the calculator. The densities come from the OxyChem Sodium Hypochlorite Handbook.
Do dichlor and trichlor add cyanuric acid?
Yes. Each ppm of chlorine from dichlor adds about 0.9 ppm of cyanuric acid (CYA), according to the Pool & Hot Tub Alliance, and trichlor adds about 0.6 ppm, worked out from its molecule. CYA protects chlorine from sunlight but is a very stable molecule, so it builds up, and the usual remedy is to drain part of the water. The 2024 MAHC keeps CYA at or below 90 ppm and keeps a pool closed at 300 ppm or more, and the CDC recommends not using cyanuric acid, or products containing it, in hot tubs. Liquid chlorine and calcium hypochlorite add none.
Is it safe to mix pool chemicals?
No. The CDC's pool chemical safety guidance says to read the entire product label or safety data sheet before use, never to mix chlorine products with acid, which can make toxic gases, and never to mix different pool chemicals, including different types of chlorine products, with each other or with any other substance. Pre-dissolve only when the label tells you to, and then add the chemical to the water, never water to the chemical, because a violent reaction can follow. Where this calculator and your label differ, follow the label.
Sources: CDC, Model Aquatic Health Code 2024 (5th Edition) Code and Annex, and “Home Pool and Hot Tub Water Treatment and Testing”; CDC, “Use Pool Chemicals Safely” poster; EPA-registered labels (calcium hypochlorite Reg. 748-295 and 748-296, sodium hypochlorite Reg. 55852-3) and EPA, Reregistration Eligibility Decision for Chlorinated Isocyanurates (1992); Pool & Hot Tub Alliance, Technical Bulletin on Dichlor; OxyChem, Sodium Hypochlorite Handbook; NIST Handbook 44. Pool gallons: pool volume calculator. Salt pools: pool salt calculator. Round and oval tanks: pond calculator. How we check our calculators.