Pool Chlorine Dosage Calculator
Calculate how much chlorine to add to raise free chlorine from current to target ppm, for liquid bleach, cal-hypo, dichlor, or trichlor products.
Result
- Free chlorine increase3 ppm
- Pure available chlorine0.376 lb
- Product needed (cal-hypo (65%))0.578 lb = 9.2 oz
Step-by-step
- Free chlorine increase needed = 3 โ 0 = 3 ppm.
- Pure chlorine = 3 ppm ร (15,000 รท 1,000,000) ร 8.345 lb = 0.376 lb.
- Adjust for product strength: 0.376 lb รท 65% = 0.578 lb = 9.2 oz of cal-hypo (65%).
How to use this calculator
- Enter the pool volume in US gallons (use a pool-volume calculator if unsure).
- Enter the current free-chlorine reading and your target (commonly 3 ppm).
- Pick the chlorine product you have โ its available-chlorine percentage is built in.
- Read the weight (and liquid volume or tablet count) to add, then re-test after circulating.
About this calculator
This calculator tells you how much chlorine product to add to raise a pool's free chlorine from its current reading to your target, typically 1โ3 ppm. The chemistry rests on one fact about water: a million US gallons weighs about 8.345 million pounds, so raising the whole pool by 1 ppm (one part per million by weight) of pure chlorine requires 8.345 pounds of chlorine per million gallons. The tool scales that to your pool volume and the desired increase, then divides by the product's available-chlorine percentage to convert pure chlorine into the actual weight of your product โ whether liquid chlorine, household bleach, cal-hypo, dichlor, or trichlor. For liquids it also gives a fluid-ounce volume, and for trichlor an approximate tablet count. Always add chlorine in the evening, run the pump, and re-test before swimming.
How it works โ the formula
ฮppm = max(0, Target โ Current)
Pure chlorine (lb) = ฮppm ร (Volume รท 1,000,000) ร 8.345
Product (lb) = Pure รท (Available% รท 100)
Product (oz) = Product lb ร 16One ppm by weight in a million gallons is 8.345 lb because that is the weight of one-millionth of a million gallons of water. Dividing by the product's available-chlorine fraction converts the pure-chlorine requirement into the dose of the actual product.
Worked examples
- Inputs:
- volume=10000, currentPpm=0, targetPpm=2, product=cal-hypo-65
- Output:
- 2 ร 0.01 ร 8.345 รท 0.65 = 0.257 lb โ 4.1 oz
- Inputs:
- volume=20000, currentPpm=1, targetPpm=3, product=liquid-12.5
- Output:
- 2 ร 0.02 ร 8.345 รท 0.125 = 2.67 lb โ 42.7 oz (โ 34 fl oz)
- Inputs:
- volume=15000, currentPpm=0, targetPpm=1, product=trichlor-90
- Output:
- 1 ร 0.015 ร 8.345 รท 0.90 = 0.139 lb โ 2.2 oz
Limitations
- Assumes the product's labelled available-chlorine percentage; old product loses strength.
- Liquid fluid-ounce figures use typical product densities and are approximate.
- Does not model chlorine demand from contaminants โ re-test after dosing.
Pool-chemistry estimate. Follow product label directions and standard safety precautions; never mix chemicals.