Calculate how much liquid chlorine to add to reach your target Free Chlorine (FC).
Enter your values and press Calculate.
This calculator estimates how much liquid chlorine is needed to raise your pool’s Free Chlorine, or FC, from the current test result to your chosen target. Enter the pool volume, current FC, target FC, and the percentage printed on the liquid chlorine label. The calculation adjusts the dose for both pool size and product strength.
Use the most accurate pool volume you have. A volume estimate that is too high can lead to overdosing, while a volume estimate that is too low may leave the pool under-sanitized. Add chlorine with the pump running, allow it to circulate, and retest before making another adjustment.
Free chlorine is the active sanitizer available to control bacteria, algae, and other contaminants. A pool can look clear and still have an unsafe chlorine level. FC is constantly being used up by sunlight, swimmers, leaves, rain, pollen, and other organic material.
The correct FC target depends heavily on the pool’s cyanuric acid, or CYA, level. As CYA rises, the pool generally needs a higher FC level to remain properly sanitized. That is why chlorine and stabilizer should always be managed together.
Use this calculator for routine chlorination, after heavy swimmer use, following a storm, before a pool party, or any time testing shows that FC is below your target. For algae treatment or a SLAM process, use the dedicated SLAM calculator because those target levels are much higher.
Allow the chlorine to circulate thoroughly. In many pools, 30–60 minutes with the pump running is enough for a useful retest, although circulation time varies by pool.
No. Liquid chlorine raises FC without adding cyanuric acid. Trichlor tablets and dichlor products add CYA along with chlorine.
Rapid chlorine loss may be caused by sunlight, low CYA, algae, ammonia, heavy contamination, or an unusually high swimmer load. Test the water rather than repeatedly adding chlorine blindly.
It is generally safer to pour it slowly in front of a return jet with the pump running, following the product label. Never mix chlorine directly with other chemicals.
If the pool repeatedly loses all its chlorine overnight, stop treating it like a normal daily-dose problem. Check for algae or another chlorine demand issue before continuing to add routine doses.