Pool chlorine calculator: find how much liquid chlorine, granular chlorine or trichlor tablets to add to reach your target free chlorine, in gallons or litres. Enter the values shown in the calculator to get a practical planning estimate.
Free interactive calculatorWater Chemistry
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FREE ONLINE CALCULATOR
Pool Chlorine Calculator
Estimate the chlorine product amount needed to raise free chlorine from your current reading to a target level.
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YOUR ESTIMATE
Estimated chlorine addition
Planning estimate
Product amount—product
Available chlorine—pounds of available chlorine
Fluid or weight detail—approximate
Free-chlorine increase—ppm
Important: Never mix chlorine products with acids or other pool chemicals. Use the exact product label, handle chemicals as directed and retest the water after circulation.
ABOUT THIS TOOL
What this calculator helps with
Water Chemistry
The pool chlorine calculator (also called a chlorine dosage calculator or chlorine dosing calculator) estimates how much chlorine to add to raise free chlorine from the current reading to your target. It works in gallons or litres and supports liquid chlorine, common granular chlorine strengths and trichlor tablets when you know the tablet weight and strength.
Why this calculation matters
Chlorine products are not interchangeable. Liquid chlorine, cal-hypo, dichlor and trichlor contain different amounts of available chlorine, so the product strength has to be part of the calculation. Dosing from a real test reading helps avoid both low sanitizer and wasteful over-treatment.
Details to have ready
Pool volume and whether it is in US gallons or litres.
Current and target free-chlorine readings in ppm.
The available-chlorine percentage printed on the exact product you are using.
Liquid product density when converting product weight to a volume (litres or gallons).
Tablet weight and strength if you are using trichlor tablets.
How to prepare
Test free chlorine, and total chlorine too if you want to check combined chlorine.
Confirm the pool volume in gallons or litres and set the units in the calculator.
Select the product and enter the strength shown on its label.
Calculate, add the chlorine as the label directs, circulate and retest.
Note: Never mix chlorine with acids or other chemicals. A calculator estimate does not replace the product label or a fresh water test.
CALCULATION GUIDE
How pool chlorine calculations work
The calculator first finds the amount of available chlorine needed for the selected free-chlorine increase, then converts that amount into your chosen product.
Available chlorine (lb) ≈ Pool volume (gallons) × Chlorine increase (ppm) ÷ 120,000 Product needed (lb) = Available chlorine ÷ (available chlorine % ÷ 100)
Liquid chlorine is also converted to an approximate fluid volume using the product density you enter. For tablets, the calculator uses the actual tablet weight and available-chlorine percentage. This makes phrases such as how much liquid chlorine to add, how much granular chlorine to use, and how many chlorine tablets to use part of the same transparent calculation.
Why product strength matters
A 12.5% liquid product does not contain the same amount of available chlorine per pound as a 6% product, and granular products use different available-chlorine strengths. Always enter the strength from the exact package you are using.
CHLORINE DOSAGE GUIDE
How much chlorine to add to a pool
Raising free chlorine by 1 part per million (ppm) in 10,000 US gallons needs about 1.3 oz of available chlorine. How much product that is depends on its strength, as the chart shows.
Chlorine needed to raise free chlorine by 1 ppm in 10,000 US gallons
Product
Available chlorine
Amount per +1 ppm
Liquid chlorine 6%
6%
17.8 fl oz
Liquid chlorine 10%
10%
10.7 fl oz
Liquid chlorine 12.5%
12.5%
8.5 fl oz
Dichlor granular 56%
56%
2.4 oz
Cal-hypo 65%
65%
2.1 oz
Cal-hypo 73%
73%
1.8 oz
Trichlor 90%
90%
1.5 oz
Multiply by the ppm increase and by pool gallons ÷ 10,000. For example, +3 ppm in a 20,000 gallon pool with 12.5% liquid chlorine is 8.5 × 3 × 2 = 51 fl oz. Liquid uses a density of 10 lb per gallon.
Chlorine calculator in litres (Australia, UK and metric pools)
Available chlorine needed (g) ≈ Pool volume (litres) × Chlorine increase (ppm) ÷ 1,000 Liquid chlorine needed (litres) = grams needed ÷ grams of available chlorine per litre on the label
A 50,000 litre pool raised by 3 ppm needs about 150 g of available chlorine. With liquid chlorine labelled 125 g/L (12.5% w/v) that is 1.2 litres. Change Volume units to litres in the calculator and it does the volume conversion for you, and you can cross-check the result with these formulas. Liquid chlorine strengths differ by country and brand, so enter the strength printed on your bottle.
Free, total and combined chlorine
Combined chlorine = Total chlorine − Free chlorine
If total chlorine is 3.0 ppm and free chlorine is 2.4 ppm, combined chlorine is 0.6 ppm. Combined chlorine is chlorine already used up on contaminants. When it is high, the pool usually needs more free chlorine or a shock. See the pool shock calculator and the guide to clearing a green pool.
Pool bleach and liquid chlorine
Liquid pool chlorine is sodium hypochlorite, the same active ingredient as household bleach, but strength varies by product and some bleaches contain additives. Pick the nearest strength in the calculator or choose Custom and enter the percentage on the label.
COMMON QUESTIONS
About Pool Chlorine Calculator
How much chlorine should I add to my pool?
The amount depends on pool volume, the current and target free-chlorine readings and the product strength. Enter those values in the calculator for an estimate. As a guide, raising free chlorine by 1 ppm in 10,000 US gallons needs about 1.3 oz of available chlorine, which is roughly 8.5 fl oz of 12.5% liquid chlorine.
How much liquid chlorine should I add to my pool in litres?
Change Volume units to litres, choose the liquid chlorine strength on your label and enter the current and target free chlorine. In grams, you need litres × ppm increase ÷ 1,000 of available chlorine. For a 50,000 litre pool raised by 3 ppm that is 150 g of available chlorine, which is about 1.2 litres of liquid chlorine labelled 125 g/L.
How do I use this chlorine calculator in Australia?
Set Volume units to litres, then enter the strength shown on your liquid chlorine label. Strength is sometimes stated as a percentage and sometimes as grams of available chlorine per litre. If your label gives g/L, you can also divide the grams of chlorine you need by that figure to get litres of product, for example 150 g ÷ 125 g/L = 1.2 litres. Always follow the label.
How much liquid chlorine does a pool need?
Choose a liquid chlorine strength and enter the product density if you want a volume conversion. The calculator first finds the available chlorine needed by mass, then converts it to an approximate liquid volume. A stronger product needs less volume, so 6% liquid chlorine takes about twice as much as 12.5%.
Is pool bleach the same as liquid chlorine?
Pool liquid chlorine is sodium hypochlorite, which is also what household bleach contains, but strengths differ between products and some bleaches contain additives. Pick the closest option or choose Custom strength and enter the percentage on the label. A pool bleach calculator uses the same maths as this one.
How do I calculate combined chlorine?
Combined chlorine is total chlorine minus free chlorine. If total chlorine reads 3.0 ppm and free chlorine reads 2.4 ppm, combined chlorine is 0.6 ppm. Combined chlorine is the part already bound to contaminants and it is commonly kept below about 0.5 ppm, so a higher reading usually means the pool needs a chlorine boost or shock. See the pool shock calculator.
How many chlorine tablets does a pool need?
Select trichlor tablet mode and enter the actual tablet weight and available-chlorine percentage. The result is an estimated tablet count for the chlorine increase you chose. Tablet sizes and strengths vary, so follow the label rather than assuming all tablets are the same.
Can this calculate chlorine for a shock treatment?
Yes, the same method estimates a larger free-chlorine increase. For a dedicated shock estimate and examples by pool size, use the pool shock calculator and always check the shock product's label.
What free chlorine level should my pool have?
The right level depends on your stabilizer (cyanuric acid) level and pool system, so no single number suits every pool. See the pool chemical ranges guide for typical targets before you set the target in the calculator.
Can I use this as a swimming pool chlorine calculator?
Yes. It supports liquid chlorine, granular products and trichlor tablets when the product strength is known, in gallons or litres.
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