Pool Shock Calculator

Safety first. Never mix pool chemicals with each other, with acid, or with anything else. Add chemicals to water, never water to chemicals. Always follow the product label. The label overrides this calculator.

Work out roughly how much chlorine product it takes to raise your pool's free chlorine from where it is now to where you want it. Pick your product, because the amount depends on how strong it is.

Enter your numbers and press Calculate.

How we calculate this

One part per million (ppm) of chlorine is 1 milligram in every liter of water.
Chlorine needed = (target ppm minus current ppm) x pool liters, in milligrams. A US gallon is 3.785 liters.
Solid products (granular): product weight = chlorine needed divided by the label's available chlorine fraction. For example 65% calcium hypochlorite is 65% available chlorine by weight.
Liquid products: we treat the label percent as grams of available chlorine per 100 mL (the usual “trade percent”), so 12.5% liquid chlorine holds 125 grams of chlorine per liter. If your label states a percent by weight instead, the true amount can differ by roughly 15%, so follow the label.

Worked example

A 15,000 gallon pool (56,781 liters) at 1 ppm that you want at 10 ppm needs 9 ppm more. That is 9 x 56,781 = 511,029 mg, or about 511 g of chlorine. With 65% calcium hypochlorite that is 511 / 0.65 = about 786 g, or 27.7 ounces of product. With 12.5% liquid chlorine it is 511 / 125 = 4.09 liters, or 138 fluid ounces.

What this tool does not cover

Chlorine demand. Sunlight, swimmers, dirt and algae use up chlorine, so the real rise may be lower than calculated. Retest after the product has circulated.
Stabilizer. Dichlor adds cyanuric acid (stabilizer) to the water with each dose. Too much stabilizer can make chlorine less effective, so test it.
Other balance. pH, alkalinity, calcium and stabilizer all matter. Test and adjust them separately.
Swimming again. Do not swim until chlorine is back in the range your label or local health department allows.
Product differences. Brands differ. Use the strength printed on your container.

Sources and further reading

CDC: Use Pool Chemicals Safely. Includes never mixing pool chemicals and adding chemical to water, never water to chemical.
CDC MMWR: Pool Chemical Injuries in Public and Residential Settings, United States, 2008 to 2017.

Last reviewed: October 27, 2026. This calculator gives estimates only and is not professional advice. Follow your product label.