Calculate liquid or granular chlorine needed to raise free chlorine, reverse-calculate the achieved ppm, or estimate pool volume from common pool shapes.
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Pool Chlorine Formula
This calculator estimates how much chlorine is needed to raise a pool’s free chlorine level by a chosen amount. The dose mode accepts current and target free chlorine, computes their difference, and reports the actual liquid or granular product quantity using its available chlorine weight percentage and, for liquids, density. Pure chlorine (Cl2 equivalent) by weight is an intermediate value shown for comparison.
- Choz = chlorine required, in ounces by weight as pure chlorine equivalent
- Vgal = pool volume, in US gallons
- Cppm = desired increase in free chlorine, in ppm
The formula works because a 1 ppm increase in water is approximately the same as adding 1 milligram per liter. The divisor 7,500 is a rounded shortcut; the conversion-based divisor is approximately 7,489.1517. The calculator uses 3.785411784 liters per US gallon and 28.349523125 grams per ounce rather than the rounded shortcut.
Equivalent Unit Forms
If you prefer metric units, the same relationship can be written in other forms:
| Pool Volume Units | Chlorine Output Units | Formula |
|---|---|---|
| US gallons | ounces | Choz ≈ (Vgal × Cppm) ÷ 7,500 |
| liters | grams | Chg = (VL × Cppm) ÷ 1,000 |
| cubic meters | kilograms | Chkg = (Vm³ × Cppm) ÷ 1,000 |
How to Calculate Pool Chlorine
- Determine the total pool volume.
- In dose mode, enter the measured current and desired target free chlorine. For example, enter 1 ppm current and 3 ppm target; the calculator derives the 2 ppm increase.
- Enter the pool volume, product form, available chlorine percentage by mass and, for a liquid, its density from the label or supplier.
- Read the result as actual product quantity: liquid volume or granular weight.
- Use the displayed chlorine-equivalent intermediate to check the product conversion. Follow the label, circulate and retest; the calculated residual is not a swimming-safety clearance.
Converting the Result to a Real Product Amount
Most pool products are not 100% chlorine. Granules, tablets, and liquid chlorine contain a certain available chlorine percentage, so the product mass is larger than the required pure chlorine equivalent unless the available fraction is 100%. Available chlorine weight percent, sodium hypochlorite weight percent and trade percent are different definitions; use the available chlorine weight basis required here.
- P = actual product amount needed
- Ch = pure chlorine equivalent from the calculator
- f = available chlorine fraction written as a decimal
Examples of decimal conversion:
- 65% available chlorine = 0.65
- 73% available chlorine = 0.73
- 90% available chlorine = 0.90
| Product Strength | Use This Conversion |
|---|---|
| 65% available chlorine | P = (Ch) / (0.65) |
| 73% available chlorine | P = (Ch) / (0.73) |
| 90% available chlorine | P = (Ch) / (0.90) |
For liquid chlorine or bleach, the exact conversion to gallons or liters depends on both the labeled strength and the solution density. The liquid calculation divides the available chlorine requirement by the available fraction and solution density. It estimates an ideal dose and does not measure chlorine demand.
Example Calculation
Suppose a pool contains 15,000 gallons of water and you want to raise free chlorine by 2 ppm.
The ideal increase requires approximately 4.005794 ounces of pure chlorine equivalent.
If the product being used contains 65% available chlorine by weight:
That means you would need about 6.16 ounces of that product by weight to supply the same chlorine increase.
Practical Notes
- Use the increase, not the goal. The formula is based on how many ppm you want to add.
- Measure volume carefully. A small error in pool volume causes the chlorine dose to be off by the same percentage.
- Circulate after dosing. Run the pump long enough for the chlorine to disperse before retesting.
- Test again after addition. Sunlight, bather load, and contaminants can consume chlorine, so measured results may differ materially from the calculated estimate.
- Keep pH and stabilizer in mind. This calculator estimates chlorine quantity only; overall sanitation performance also depends on broader water balance.
Common Input Mistakes
- Selecting gallons when the pool volume is actually in liters
- Entering an increase in the target field instead of the desired final level
- Confusing liquid fluid ounces with granular ounces by weight
- Ignoring product strength when converting from pure chlorine equivalent
This calculator estimates an ideal product dose or concentration change, not chlorine demand, breakpoint chlorination or a treatment for contamination. Never mix pool chemicals; follow the product label and local requirements, circulate and retest before use.
