Pool Chlorine Dose Calculator
One ppm is one mg/L, so raising 1,000 litres by 1 ppm takes exactly 1 gram of pure available chlorine. That part is easy — the part people get wrong is that shops do not sell pure chlorine, so the weight has to be divided again by the product strength. Taking 50,000 litres from 1 ppm to 3 ppm needs 100 g of pure available chlorine, which is 800 of a 12.5% product. Liquid chlorine states its percentage as grams per 100 mL rather than by weight, so reading that 800 as grams for granular and as millilitres for liquid is correct either way.
Your numbers
Product to add
800g
As pure available chlorine
100g
Product per 1 ppm
400g
What it means
Raising by 2 ppm takes 800 of product — grams for granular, and the same number as millilitres for liquid, whose percentage is stated per 100 mL.
Formula
As pure available chlorine = Litres × (Free chlorine wanted − Free chlorine now) ÷ 1000, Product to add = As pure available chlorine ÷ (Product strength ÷ 100)
Free chlorine only works as hard as your stabiliser level allows: high cyanuric acid blunts it, and the target has to move up to compensate. Chlorine also cannot be removed once added, so dose half, wait, and retest rather than jumping straight to target.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Litres (L)Capacity in litres; one litre is 1,000 cm³. | 50,000 | 0 and up |
| Free chlorine now (ppm)The free chlorine in the water right now, as read by a test kit or strip. | 1 | 0 ~ 30 |
| Free chlorine wanted (ppm)The free chlorine you are aiming at; high stabiliser means aiming higher for the same effect. | 3 | 0 ~ 30 |
| Product strength (%)The available chlorine in the product — by weight for granular, per 100 mL for liquid. | 12.5 | 0 ~ 100 |
Step by step
Quick reference table
Results when only Litres (L) changes and everything else stays put.
| Litres (L) | Product to add (g) | As pure available chlorine (g) | Product per 1 ppm (g) |
|---|---|---|---|
| 25,000 | 400 | 50 | 200 |
| 37,500 | 600 | 75 | 300 |
| 50,000 | 800 | 100 | 400 |
| 75,000 | 1,200 | 150 | 600 |
| 100,000 | 1,600 | 200 | 800 |
What each result means
| Result | At default values |
|---|---|
| Product to add (g)How much to scoop or pour out — measured as product, not as pure chlorine. | 800 |
| As pure available chlorine (g)The weight of pure available chlorine alone, which is how products compare fairly. | 100 |
| Product per 1 ppm (g)The product this pool needs per 1 ppm — from then on you just multiply. | 400 |
Common mistakes
Free chlorine only works as hard as your stabiliser level allows: high cyanuric acid blunts it, and the target has to move up to compensate. Chlorine also cannot be removed once added, so dose half, wait, and retest rather than jumping straight to target.
Glossary
- Litres
- Capacity in litres; one litre is 1,000 cm³.
- Free chlorine now
- The free chlorine in the water right now, as read by a test kit or strip.
- Free chlorine wanted
- The free chlorine you are aiming at; high stabiliser means aiming higher for the same effect.
- Product strength
- The available chlorine in the product — by weight for granular, per 100 mL for liquid.
- Product to add
- How much to scoop or pour out — measured as product, not as pure chlorine.
- As pure available chlorine
- The weight of pure available chlorine alone, which is how products compare fairly.
- Product per 1 ppm
- The product this pool needs per 1 ppm — from then on you just multiply.
Frequently asked questions
Q. How is Pool Chlorine Dose Calculator calculated?
As pure available chlorine = Litres × (Free chlorine wanted − Free chlorine now) ÷ 1000, Product to add = As pure available chlorine ÷ (Product strength ÷ 100) — One ppm is one mg/L, so raising 1,000 litres by 1 ppm takes exactly 1 gram of pure available chlorine. That part is easy — the part people get wrong is that shops do not sell pure chlorine, so the weight has to be divided again by the product strength. Taking 50,000 litres from 1 ppm to 3 ppm needs 100 g of pure available chlorine, which is 800 of a 12.5% product. Liquid chlorine states its percentage as grams per 100 mL rather than by weight, so reading that 800 as grams for granular and as millilitres for liquid is correct either way.
Q. Can you walk through an example?
With Litres 50,000L, Free chlorine now 1ppm, Free chlorine wanted 3ppm, Product strength 12.5%, the answer is Product to add 800g.
Q. What do I need to enter?
Enter Litres, Free chlorine now, Free chlorine wanted, Product strength. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Litres (L) moves the answer to Litres (L) 25,000 → Product to add (g) 400 and Litres (L) 100,000 → Product to add (g) 1,600. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Free chlorine only works as hard as your stabiliser level allows: high cyanuric acid blunts it, and the target has to move up to compensate. Chlorine also cannot be removed once added, so dose half, wait, and retest rather than jumping straight to target.
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