Pool Chlorine Dose (ppm) Calculator
Work out exactly how much chlorine product to add to raise your pool from its current free-chlorine level to a target ppm.
How it works
Pure chlorine (lb) = Δppm × gallons × 8.34 ÷ 1,000,000 · Product (lb) = pure ÷ (available % ÷ 100)
Chlorine dose is pure mass-balance: one part per million means one pound of chlorine for every million pounds of water, and a US gallon of water weighs 8.34 lb. Multiply the ppm you want to add by the gallons and by 8.34, divide by a million, and you have the pounds of 100% chlorine required. Because real products are only partly chlorine, you then divide by the product’s available-chlorine fraction — cal-hypo is 65%, trichlor 90%, liquid bleach around 12.5% — to get the actual weight to scoop or pour in.
Worked example
To lift a 10,000-gallon pool from 1 ppm to 3 ppm you need 2 ppm of chlorine: 2 × 10,000 × 8.34 ÷ 1,000,000 = 0.167 lb of pure chlorine. Using 65% cal-hypo that is 0.167 ÷ 0.65 = 0.257 lb, or about 4.1 oz.
Frequently asked questions
Does this work for liquid chlorine?
Yes — pick the 12.5% liquid-bleach option and the result is the weight of solution; since a gallon of 12.5% liquid chlorine weighs roughly 10 lb you can divide the ounces by about 10.4 to get fluid ounces. The mass math is identical whatever the form.
Why did my chlorine barely move after dosing?
Chlorine demand — organics, sunlight and bather load consume free chlorine as fast as you add it. If a correct dose does not register, the pool has high demand and may need shock-level chlorination, and an unstabilised pool loses chlorine quickly to UV without cyanuric acid.
Is ppm the same as mg/L?
For dilute water chemistry, yes: 1 ppm equals 1 milligram per litre because a litre of water masses almost exactly 1,000 grams. Pool test kits report free chlorine directly in ppm.
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This calculator is for educational purposes. Double-check important results before acting on them.