Pool Salt Calculator
Salinity is measured in ppm just like chlorine, so the arithmetic is identical — only the scale differs. One ppm is one mg/L, so raising a litre by 1,000 ppm takes a gram, and raising 50,000 litres by 2,400 ppm takes 120 kg, or six 20 kg bags. Salt is close to pure, so there is no second division by product strength the way there is with chlorine. What is worth knowing instead is how far one bag moves your pool: here each bag is worth 400 ppm, which is enough for the last bag to overshoot the target on its own.
Your numbers
Salt to add
120kg
Bags needed
6bags
Salinity one bag adds
400ppm
What it means
You need 120 kg of salt, and one bag moves this pool by 400 ppm — retest before you tip in the last one.
Formula
Salt to add = Litres × (Salinity wanted − Salinity now) ÷ 1,000,000, Bags needed = ⌈Salt to add ÷ Bag weight (kg)⌉
Most chlorinators run somewhere between 2,700 and 3,400 ppm and the right figure is the one in your cell manual, not a general rule. Run the pump while you add it, and pour along the shallow end floor and brush it in rather than down the skimmer, so undissolved salt never reaches the cell.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Litres (L)Capacity in litres; one litre is 1,000 cm³. | 50,000 | 0 and up |
| Salinity now (ppm)The salinity now; a chlorinator readout drifts, so an independent test is safer. | 800 | 0 ~ 10,000 |
| Salinity wanted (ppm)The salinity you are aiming at — take it from your cell manual, not a general rule. | 3,200 | 0 ~ 10,000 |
| Bag weight (kg)The weight of one bag; 20, 25 and 40 kg are common and printed on the front. | 20 | 0 and up |
Step by step
Quick reference table
Results when only Litres (L) changes and everything else stays put.
| Litres (L) | Salt to add (kg) | Bags needed (bags) | Salinity one bag adds (ppm) |
|---|---|---|---|
| 25,000 | 60 | 3 | 800 |
| 37,500 | 90 | 5 | 533 |
| 50,000 | 120 | 6 | 400 |
| 75,000 | 180 | 9 | 267 |
| 100,000 | 240 | 12 | 200 |
What each result means
| Result | At default values |
|---|---|
| Salt to add (kg)The salt to add to reach target; salt is near pure, so no strength division applies. | 120 |
| Bags needed (bags)How many bags to buy; they are not sold in fractions, so this rounds up. | 6 |
| Salinity one bag adds (ppm)How far one bag moves this pool — it tells you whether the last bag overshoots. | 400 |
Common mistakes
Most chlorinators run somewhere between 2,700 and 3,400 ppm and the right figure is the one in your cell manual, not a general rule. Run the pump while you add it, and pour along the shallow end floor and brush it in rather than down the skimmer, so undissolved salt never reaches the cell.
Glossary
- Litres
- Capacity in litres; one litre is 1,000 cm³.
- Salinity now
- The salinity now; a chlorinator readout drifts, so an independent test is safer.
- Salinity wanted
- The salinity you are aiming at — take it from your cell manual, not a general rule.
- Bag weight (kg)
- The weight of one bag; 20, 25 and 40 kg are common and printed on the front.
- Salt to add
- The salt to add to reach target; salt is near pure, so no strength division applies.
- Bags needed
- How many bags to buy; they are not sold in fractions, so this rounds up.
- Salinity one bag adds
- How far one bag moves this pool — it tells you whether the last bag overshoots.
Frequently asked questions
Q. How is Pool Salt Calculator calculated?
Salt to add = Litres × (Salinity wanted − Salinity now) ÷ 1,000,000, Bags needed = ⌈Salt to add ÷ Bag weight (kg)⌉ — Salinity is measured in ppm just like chlorine, so the arithmetic is identical — only the scale differs. One ppm is one mg/L, so raising a litre by 1,000 ppm takes a gram, and raising 50,000 litres by 2,400 ppm takes 120 kg, or six 20 kg bags. Salt is close to pure, so there is no second division by product strength the way there is with chlorine. What is worth knowing instead is how far one bag moves your pool: here each bag is worth 400 ppm, which is enough for the last bag to overshoot the target on its own.
Q. Can you walk through an example?
With Litres 50,000L, Salinity now 800ppm, Salinity wanted 3,200ppm, Bag weight (kg) 20, the answer is Salt to add 120kg.
Q. What do I need to enter?
Enter Litres, Salinity now, Salinity wanted, Bag weight (kg). 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 → Salt to add (kg) 60 and Litres (L) 100,000 → Salt to add (kg) 240. 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?
Most chlorinators run somewhere between 2,700 and 3,400 ppm and the right figure is the one in your cell manual, not a general rule. Run the pump while you add it, and pour along the shallow end floor and brush it in rather than down the skimmer, so undissolved salt never reaches the cell.
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