About the Pool Chlorine Calculator
This pool chlorine calculator tells you exactly how much chlorine product to add to raise your free chlorine (FC) from its current reading to a target level. Enter your pool volume in gallons, the current and target free chlorine in ppm, and the product you use — liquid chlorine, household bleach, calcium hypochlorite (cal-hypo) shock, dichlor or trichlor.
It is built for pool owners doing daily top-ups and for shocking after a party, a storm or an algae outbreak. Liquid doses are shown in fluid ounces and gallons; dry products in ounces and pounds by weight. Because stabilizer (cyanuric acid, CYA) makes chlorine less active, the tool also shows a commonly used minimum and shock level based on your CYA reading.
Liquid pool chlorine is sold by "trade percent" (grams of available chlorine per 100 mL). Household bleach is labeled as percent sodium hypochlorite by weight, which works out within a few percent of the same figure, so it is treated the same way here. Both lose strength as they age, so old product may need more. Always retest after circulating and never mix different chlorine products together.
With the default inputs, the amount to add is 30.7 oz. Change any value above to recalculate instantly.
How to use the pool chlorine calculator
- 1Test your water and note the free chlorine and CYA readings.
- 2Enter your pool volume in gallons (use the pool volume calculator if unsure).
- 3Set the target free chlorine — use the shock level to clear algae.
- 4Choose the product you have and read off the dose.
- 5Pour it in front of a return jet with the pump running, then retest after an hour.
Formula and method
One ppm is one milligram of chlorine per liter of water, which equals 8.345 millionths of a pound per gallon. Multiplying the required rise in ppm by the pool volume gives the pounds of available chlorine needed; dividing by the product strength gives the pounds of dry product.
Liquid chlorine strength is given in trade percent (grams of available chlorine per 100 mL; bleach labels in weight percent are close enough to use directly), so one gallon of 12.5% chlorine raises 10,000 gallons by 12.5 ppm. The recommended levels use the widely used guideline of free chlorine at about 7.5% of CYA as a minimum and 40% of CYA for shocking.
- Δppm
- Target free chlorine minus current free chlorine
- Strength %
- Available chlorine percentage of the product
- 8.345×10⁻⁶
- Pounds per gallon for 1 ppm in water
Worked examples
Raise 15,000 gal from 1 to 3 ppm with 12.5% liquid
A 2 ppm rise in 15,000 gallons needs 2 × 15,000 ÷ 125,000 = 0.24 gallons of 12.5% liquid chlorine, which is about 30.7 fl oz. With 40 ppm CYA the recommended minimum is 3 ppm and the shock level 16 ppm.
Shock 20,000 gal to 10 ppm with 65% cal-hypo
Raising 20,000 gallons by 10 ppm needs 10 × 20,000 × 8.345×10⁻⁶ ≈ 1.67 lb of available chlorine. At 65% strength that is 2.57 lb of cal-hypo, or about 41 ounces.
Top up 10,000 gal by 3 ppm with 6% bleach
A 3 ppm rise in 10,000 gallons with 6% bleach needs 3 × 10,000 ÷ 60,000 = 0.5 gallons — 64 fluid ounces.
Frequently asked questions
How much liquid chlorine raises a pool by 1 ppm?+
About 10.2 fl oz of 12.5% liquid chlorine raises 10,000 gallons by 1 ppm. With 10% chlorine it is about 12.8 fl oz, and with 6% household bleach about 21.3 fl oz.
What should my free chlorine level be?+
Many pool owners keep free chlorine at 1–3 ppm in unstabilized pools, but stabilizer changes this. A widely used guideline is to keep free chlorine at least 7.5% of your cyanuric acid level, so 40 ppm CYA calls for about 3 ppm FC.
How much shock do I need to kill algae?+
Algae is usually cleared by holding free chlorine at a shock level of about 40% of the CYA reading until the water is clear and overnight chlorine loss is under 1 ppm. With 30 ppm CYA that means about 12 ppm.
Can I use household bleach in my pool?+
Yes, plain unscented bleach is the same sodium hypochlorite as pool liquid chlorine, just weaker (often 6–8.25%). Avoid scented, splash-less or "outdoor" formulas that contain additives.
How long after adding chlorine can I swim?+
After a normal top-up, wait until it has circulated for at least 20–30 minutes and retest. After shocking, wait until free chlorine falls back to a normal level for your CYA before swimming.