Pool Chlorine Calculator
Calculate how much chlorine to add to hit your target free chlorine level, whether you use liquid chlorine, household bleach, cal-hypo, or dichlor granules.
Estimates assume listed product strength; actual strength fades with product age. Add with the pump running, never mix chlorine products with each other or with acid, and always follow the product label. Retest after 30 to 60 minutes of circulation.
How chlorine dosing works
Every chlorine product is rated by its available chlorine percentage. The higher the percentage, the less product you need to raise free chlorine (FC) by the same amount. This calculator uses standard dosing factors per 10,000 gallons:
factors: 12.5% liquid = 10.2 fl oz · 10% bleach = 12.8 fl oz
67% cal-hypo = 2.0 oz weight · 56% dichlor = 2.4 oz weight
Your pool volume drives everything, if you are not sure of yours, run it through the pool volume calculator first. A 20 percent volume error means a 20 percent dosing error every single time.
Worked example: raising FC from 1 to 4 ppm
For a 15,000 gallon pool using 12.5 percent liquid chlorine:
- Needed increase: 4 − 1 = 3 ppm
- Volume factor: 15,000 / 10,000 = 1.5
- Dose: 3 x 1.5 x 10.2 = about 46 fl oz
- That is roughly a third of a gallon jug
Maintenance dosing vs shocking
Routine maintenance means keeping FC in the 1 to 4 ppm range (higher if your CYA is high). Shocking means deliberately spiking FC to roughly 10 times your combined chloramine reading, typically 10 to 12 ppm or more, to kill algae and burn off contamination. Both use the same math; only the target changes. Shock at dusk so the sun does not immediately burn off your investment, and keep the pump running overnight.
Safety rules that are not optional
- Never mix chlorine types with each other, or any chlorine with acid.
- Add product to the pool, never water to concentrated product.
- Pre-dissolve granular products in a bucket of pool water if your label says to.
- Store liquid chlorine cool and shaded; it loses strength fast in heat.
- Wait for FC to drop below 5 ppm before swimming after a shock.
Frequently asked questions
How much liquid chlorine do I add to a 15,000 gallon pool?
To raise free chlorine by 3 ppm in 15,000 gallons, add about 46 fl oz (roughly a third of a gallon) of 12.5 percent liquid chlorine. To shock to 12 ppm from 1 ppm, you would need about 168 fl oz, or 1.3 gallons.
What free chlorine level should I maintain?
The widely used guidance is 1 to 4 ppm for residential pools, but the right target depends on your stabilizer (CYA) level: higher CYA requires proportionally higher free chlorine to sanitize effectively. A common rule of thumb is free chlorine at about 7.5 percent of your CYA reading.
What is the difference between liquid chlorine and bleach?
Chemically they are the same sodium hypochlorite. Pool liquid chlorine is typically 10 to 12.5 percent strength, household bleach 5 to 8 percent. Avoid scented or splashless bleach, the additives do not belong in pool water.
When should I use cal-hypo vs dichlor vs liquid?
Liquid chlorine adds nothing but chlorine and a little salt, making it the default choice. Cal-hypo adds calcium, useful if your calcium hardness is low, a problem if it is already high. Dichlor adds CYA stabilizer, roughly 0.9 ppm CYA per 1 ppm of chlorine, which builds up fast and is best reserved for new fills that need stabilizer anyway.
Why does my chlorine disappear so fast?
The usual culprits: little or no CYA stabilizer (UV sunlight destroys unstabilized chlorine within hours), a heavy organic load such as algae beginning to bloom, or hot weather with heavy bather use. If chlorine vanishes overnight with no sun, suspect algae and consider shocking.