Start with a salinity reading
A salt chlorine generator works within a manufacturer-specified salinity range. The amount of salt to add depends on both the water already in the pool and the dissolved salt already present. Measure salinity before using this calculator, then enter the target from your generator manual. The example target is simply a sample input. Pool salt is not automatically needed whenever water looks cloudy or a chlorine reading is low; those symptoms can have other causes. This tool estimates a mass addition from concentration and volume.
Convert parts per million to kilograms
Salt addition (kg) = water volume (litres) × max(0, target ppm − current ppm) ÷ 1,000,000For this practical pool-water calculation, one part per million is treated as one milligram of salt per litre. Multiply that concentration difference by the number of litres, then convert milligrams to kilograms. Imperial mode uses US gallons, with 3.785411784 litres per gallon, and converts kilograms to pounds using 0.45359237 kilograms per pound. The bag count rounds up for purchasing, but the actual mass to add remains the unrounded requirement. There is no waste margin: intentionally overshooting the target is not part of the calculation.
Example: raising salinity by 2,000 ppm
A pool containing 40 cubic metres holds 40,000 litres. A measured concentration of 1,000 ppm and an equipment target of 3,000 ppm leave a 2,000 ppm difference. Required salt is 40,000 × 2,000 ÷ 1,000,000 = 80 kilograms. With 25 kilogram bags, buy four bags but add only 80 kilograms, keeping the unused balance. A pool with 10,000 US gallons requires approximately 166.91 pounds for the same concentration increase. Five 40 pound bags cover that requirement, although emptying all five bags would exceed the calculated addition.
Check volume and add in stages
Use the actual operating water level rather than the pool's nominal external dimensions. Steps, benches and a shallow end reduce the volume, while a connected water-filled system may increase it. An inaccurate volume estimate directly changes the salt requirement. Follow the equipment instructions for distributing salt, circulation and waiting before retesting. Adding a portion and checking the dissolved reading reduces the chance of overshooting. If current salinity is at or above the target, the tool returns zero addition. It does not calculate dilution or recommend draining; those depend on water balance and the installation. Avoid using bag count as a dosing instruction, since purchased bags are rounded up while the concentration equation is not.
Frequently asked questions
How much salt raises 40 m³ by 1000 ppm?
Forty cubic metres contain 40,000 litres. A 1000 ppm increase needs 40 kilograms of salt under the dilute-water approximation used here.
Is the gallon US or imperial?
The volume field uses US gallons. A British imperial gallon is larger, so convert that measurement before entering it.
Should I add every bag I buy?
No. Bags are rounded up for purchasing. Measure out the mass shown as Salt to add and keep any surplus for later use.
What if current ppm exceeds the target?
The required addition is zero. This tool does not remove salt or calculate a draining plan; consult the equipment instructions for high salinity.
What target should I choose?
Use the range specified by your own salt chlorine generator. The default is a worked example and does not override its manual.
Last reviewed: 2026-10-03 · How we calculate