How This Chlorine Calculator Works
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.
Why Free Chlorine Matters
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.
When to Use This Tool
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.
Common Chlorine-Dosing Mistakes
- Guessing the pool volume instead of calculating it.
- Using the wrong liquid-chlorine strength.
- Ignoring the pool’s CYA level when choosing an FC target.
- Adding a large dose without circulating and retesting.
- Mixing chlorine with acid or other pool 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.