Pool & spa
Pool Salt Calculator
Doses salt for a chlorine generator, where the cell needs a specific range to work.
Result
Dose against a test result, never against a schedule. Add chemicals in stages with the pump running, wait for a full turnover, then retest before adding more. Never mix chemicals, and never add water to acid. Where a product label differs from the figure here, the label wins. Salt is not consumed, only diluted by rain and splash-out or lost through backwashing, so it needs topping up rarely. Running a cell below its minimum salinity damages it, and running above the maximum is corrosive; both limits come from the cell manufacturer rather than a general figure.
Get a Free Business AuditHow the calculation works
The dose is the gap between current and target salinity times the volume, converted to pounds of salt. A salt chlorine generator electrolyses dissolved salt into chlorine, and it needs the salinity within the range its cell is designed for: too low and it cannot produce, too high and it can damage the cell and corrode fittings. Salt is not consumed by chlorine generation, so it only needs topping up for water lost to splash-out, backwashing and drainage, not for sanitising.
What moves the number
- Current salinity against the cell's required range.
- Volume, which scales the dose.
- Water loss since the last addition, since that is what reduces salinity.
- Whether the salt is the correct grade for pool use.
Where this one goes wrong
Salt is not used up by making chlorine, which surprises owners who expect to add it continually. It leaves only with water, so a pool that needs salt regularly is losing water, through splash-out, backwashing, a leak or drainage, and a persistent salt demand is worth investigating as a water loss rather than a chemical one. Over-salting is corrected only by dilution, so dose conservatively and retest. Use salt graded for pool use rather than rock salt or table salt, since the additives and impurities in those can stain surfaces and foul the cell.
Before you quote
- Investigate a recurring salt demand as a water loss.
- Dose conservatively, since over-salting is corrected by dilution.
- Use pool grade salt, not rock or table salt.
Where the rules come from
Questions
About this calculator
Does salt get used up making chlorine?
No. The process converts salt to chlorine and the chlorine reverts to salt, so it recycles. Salt only leaves with water, through splash-out, backwashing, leaks and drainage. A pool needing salt regularly is losing water, which is worth investigating rather than topping up indefinitely.
What happens if salinity is too high?
It can damage the generator cell and accelerate corrosion of metal fittings, ladders and some stone coping. It is also only correctable by dilution, so there is no quick fix. That makes conservative dosing and retesting the right approach rather than aiming for the top of the range.
Can I use any salt?
Pool grade salt only. Rock salt and table salt contain additives and impurities, including anti-caking agents and iodine, that can stain surfaces and foul the generator cell. The price difference is small relative to a cell replacement.
The formula
about 8.35 lb of salt per 10,000 gallons raises salinity 100 ppm
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How to use this calculator
- Pool volume (gallons). Enter your own figure; the page starts at 20,000.
- Current salt (ppm). Enter your own figure; the page starts at 2,400.
- Target salt (ppm). Enter your own figure; the page starts at 3,200.
- Price per pound or gallon ($). Enter your own figure; the page starts at $0.22.
The result updates as you type, so you can try a figure, see what it does to salt to add, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Pool volume (gallons) | 20,000 |
| Current salt (ppm) | 2,400 |
| Target salt (ppm) | 3,200 |
| Price per pound or gallon | $0.22 |
What comes out
| Result | Value |
|---|---|
| Salt to add main result | 133.6 |
| Change needed | 800.0 |
| Estimated cost | $29.39 |
| Dose per 10,000 gallons | 66.8 |
Add about 133.6 to move 20,000 gallons from 2400 to 3200.
How sensitive the answer is
Holding everything else steady and changing only price per pound or gallon, this is what happens to salt to add. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Price per pound or gallon ($) | Salt to add |
|---|---|
| $0.11 | 133.6 |
| $0.17 | 133.6 |
| $0.22 example above | 133.6 |
| $0.33 | 133.6 |
| $0.44 | 133.6 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Pool volume (gallons)
- A number, between 0 and 2000000, starting at 20,000.
- Current salt (ppm)
- A number, between 0 and 6000, starting at 2,400.
- Target salt (ppm)
- A number, between 0 and 6000, starting at 3,200.
- Price per pound or gallon ($)
- A money amount, starting at $0.22.
What the results tell you
| Result | What it is |
|---|---|
| Salt to add | The headline result. A decimal figure. |
| Change needed | A decimal figure. |
| Estimated cost | A money figure. |
| Dose per 10,000 gallons | A decimal figure. |
Keep going
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