About this tool
The Saltwater Pool Salt Calculator is a free, in-browser tool that tells you how much pool salt to add so your salt-chlorine generator (SWG) runs at its ideal salinity. Salt cells make chlorine from dissolved salt, and most units want the water around 3,200 ppm (a typical acceptable band is 2,700–3,400 ppm). The dose to raise salinity is lb = gallons × Δppm ÷ 120,000 (equivalently gallons × 8.34 × Δppm ÷ 1,000,000); in metric it is kg = litres × Δppm ÷ 1,000,000.
All of the arithmetic runs locally in your browser, so nothing you type leaves your device. Enter your pool volume, current salinity, and target salinity, and the tool returns the salt to add in pounds plus the number of 40 lb bags (US) or kilograms plus 25 kg bags (metric), rounding up so you buy enough. Add salt gradually with the pump running, brush it to dissolve, and wait about 24 hours before retesting and turning the cell to full output.
Salt, like cyanuric acid, cannot be removed chemically — if the water is over-salted the only fix is to drain and dilute. When your target is below the current reading the calculator switches to dilution mode and reports the fraction of water to drain and refill: drain fraction = 1 − target ÷ current. This is handy after heavy rain, an accidental double dose, or when swapping to a cell that wants a lower level.