Pool Volume Calculator
Gallons and litres for rectangular or round pools.
Pool & Recreation
Pool Salt Calculator
Salt needed to bring a saltwater pool up to the level your chlorine generator asks for, from the pool volume and a current reading.
Your result
Sample values534
Pounds of salt
14
Bags
3,200
Increase, ppm
20,000
Pool volume, gallons
20,000 gallons from 0 to 3,200 ppm, 40 lb bags.
Typical target ranges
| Chlorinator | Target |
|---|---|
| Common range | 2,700 – 3,400 ppm |
| Frequent default | 3,200 ppm |
| Taste threshold | about 3,500 ppm |
| Check | Your own manual |
How to use this calculator
Enter the pool volume in gallons and test the water for its current salt level. The calculator works out the shortfall against your target and converts that to pounds of salt.
The target is the number your chlorine generator asks for, and it varies between manufacturers. Three thousand two hundred parts per million is a common default but it is not universal — a unit set up for 2,700 will alarm at 3,400, so use the figure in your own manual rather than the one filled in here.
Formula
Shortfall = Target − Current
Water weight = Volume × 8.345 lb/gal
Salt = Water weight × Shortfall ÷ 1,000,000
Bags = ceil(Salt ÷ Bag size)
- ppm
- parts per million by weight — 1 ppm is 1 mg per litre
- 8.345
- pounds in a US gallon of water
Salt is not consumed by the generator. It only leaves through splash out, backwashing and rain overflow.
Worked example
A 20,000 gallon pool on a fresh fill, targeting 3,200 ppm, 40 lb bags.
- Shortfall: 3,200 − 0 = 3,200 ppm
- Water weight: 20,000 × 8.345 = 166,900 lb
- Salt: 166,900 × 3,200 ÷ 1,000,000 = 534 lb
- Bags: 534 ÷ 40 = 13.4, so 14 bags
534 lb of salt, or 14 bags
Understanding your results
Salt does not get used up. The generator splits it into chlorine, that chlorine does its job and reverts to salt, and the cycle repeats. Levels only fall through water leaving the pool — splash out, backwashing, and rain pushing water over the skimmer. That is why a pool needs topping up occasionally rather than dosing on a schedule.
Going over the target is much harder to fix than going under. There is no way to remove salt from water except to drain some of it and refill, so add about three quarters of the calculated amount, let it circulate for a day, then test and top up.
Questions
About this calculator
Whatever your chlorine generator specifies, which is usually somewhere between 2,700 and 3,400 ppm. There is no universal figure, and running outside your unit’s range either shuts it down or shortens the cell life. The manual is the only authority here.
Give it at least 24 hours with the pump running. Salt takes time to dissolve and distribute, and testing too early reads low, which tempts people into adding a second dose they did not need.
Pool grade sodium chloride, at least 99.8% pure and free of anti-caking agents and iodine. Water softener salt is usually acceptable if it meets that purity; rock salt and table salt are not, because the additives stain surfaces.
The only remedy is dilution: drain part of the pool and refill with fresh water. Nothing removes salt chemically. The calculator returns zero rather than a negative figure when your current level is already above target.
Keep going
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Estimates, not specifications.
Results are based on the values you enter and on typical material
properties. Densities, coverage rates and product sizes vary between
suppliers, so confirm quantities against your supplier's data before
ordering. Structural work must be signed off by a qualified
professional and meet your local building code.