Pool Salt Calculator (Kilos of Salt for a Saltwater Pool)
Kilograms of salt to add to a swimming pool to go from its current salt level to the one your chlorinator needs, and how many bags that is.
Results
What this tool does
A part per million of salt is a milligram in each kilogram of water, and a cubic metre of water weighs about 1000 kg, so every 1000 ppm you want to add takes 1 kg of salt per cubic metre. A 50 m³ pool going from 400 to 3200 ppm needs 140 kg. The target depends on the chlorinator, so check its manual rather than a general figure: pools of this kind usually run at around 3000 ppm, which is under a tenth of the saltiness of seawater. Add the salt gradually, with the pump running, and test again after the water has circulated before adding more.
Formula
salt (kg) = pool volume (m³) × (target ppm − current ppm) ÷ 1000
Variables
| Symbol | Meaning | Unit |
|---|---|---|
v | Pool volume | m³ |
cu | Salt in the water now | ppm |
tg | Salt level you want | ppm |
bg | Size of a bag of salt | kg |
KG | Salt to add | kg |
BG | Bags to buy | — |
Worked example
- Pool volume50 m³
- Salt in the water now400 ppm
- Salt level you want3200 ppm
- Size of a bag of salt25 kg
- Salt to add140.0 kg
- Bags to buy6
Limitations
- These are parts per million by mass. In water at ordinary temperatures 1 ppm is also 1 mg/L, because a litre of water weighs about a kilogram, but that equivalence fails for any other liquid and for gases.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.