Pool Shock Calculator

Free chlorine is measured in parts per million by mass, so the shock a pool needs is the weight of the water times the gap you are closing, divided by the available chlorine in the product. Enter the volume in gallons, the current and target free chlorine readings and the product you are using, and the tool returns the weight or the volume to add with the working shown. A second tab takes a combined chlorine reading instead and works to the conventional breakpoint of ten times that figure. Every result names the product strength it assumed and what that product leaves behind, because calcium, cyanuric acid and salt all build up and only replacing water removes them.

Calculator Type
Units
The pool volume is read in the unit you pick here, and the dose comes back in it too.

From a free chlorine reading to the level you want, for a product whose available chlorine percentage you pick.

Water volume, in the unit you chose above: 100 to 1,000,000 US gallons, which is 379 to 3,785,412 litres. The pool volume calculator works it out from the dimensions.
From a test kit, taken now. A strip that has been in the sun is not a reading.
The level you are aiming for. Take it from the product label or your own testing routine.
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Units
The pool volume is read in the unit you pick here, and the dose comes back in it too.

Combined chlorine is total chlorine minus free chlorine. Breakpoint chlorination is conventionally worked as free chlorine ten times that reading.

Water volume, in the unit you chose above: 100 to 1,000,000 US gallons, which is 379 to 3,785,412 litres. The pool volume calculator works it out from the dimensions.
Total chlorine minus free chlorine, from a test that reports both. The smell people call a chlorine smell is this, not free chlorine.
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Related Tools
Pool Volume Calculator Pool Salt Calculator