Pool Salt Calculator

Salt chlorine generators only work within a narrow salt range — often around 2,700 to 3,400 ppm, depending on the manufacturer. Enter your pool volume (or its size), the current salt reading and your chlorinator’s target, and the calculator tells you how many 40 lb bags to add, or how much water to replace if the level is too high.

How the calculation works

Salt concentration in parts per million (ppm) is milligrams of salt per litre — or pounds per million pounds of water. A US gallon of water weighs about 8.34 lb, so the salt needed is: pounds = gallons × 8.34 × (target ppm − current ppm) ÷ 1,000,000. In metric, a litre of water weighs about 1 kg, so kilograms = litres × (target − current) ÷ 1,000,000. For a 20,000-gallon pool raised from 2,400 to 3,200 ppm, that is 20,000 × 8.34 × 800 ÷ 1,000,000 ≈ 133 lb — just over three 40 lb bags.

Pool volume formulas

Average depth is the shallow depth plus the deep depth divided by two. For pools with a large shallow area, weight the average towards the shallow depth. Your pool builder’s documents or the chlorinator installation records may list the exact volume.

Target salt levels

Every salt chlorine generator has a recommended range — commonly somewhere between about 2,700 and 3,400 ppm, with an ideal around 3,000–3,200 ppm for many popular models, but some systems are designed for lower or higher levels. Always use the figure in your chlorinator’s manual. Too little salt makes the cell work harder and produce less chlorine; too much can trigger alarms, shut the cell down or increase corrosion risk for metal fittings.

How to add salt

1. Test the salt level with test strips or a digital meter, and check the chlorinator’s reading too.
2. Turn the salt chlorinator off (the pump stays on).
3. Pour the salt around the shallow end or the perimeter, away from the skimmer and main drain.
4. Brush the salt towards the deep end to help it dissolve.
5. Run the pump for 24 hours to circulate the water.
6. Retest, then switch the chlorinator back on.

Worked example

A 32 × 16 ft rectangular pool, 3.5 ft deep at the shallow end and 6 ft at the deep end, has an average depth of 4.75 ft and a volume of about 18,190 gallons. Raising it from 2,400 to 3,200 ppm needs 18,190 × 8.34 × 800 ÷ 1,000,000 ≈ 121 lb, or four 40 lb bags (3.0 bags exactly — buying four covers a little extra).

When salt drops

• Splash-out and backwashing remove salty water.
• Heavy rain dilutes the pool.
• Draining to lower cyanuric acid or calcium removes salt too.
• Salt does not evaporate — topping up with fresh water after evaporation keeps the level the same.

Testing salt accurately

Salt chlorinators estimate salt from the cell’s electrical conductivity, and readings drift as the cell ages or scales up. Confirm the reading with salt test strips or a digital salinity meter before adding a large amount, and test after the pump has run for a while so the water is well mixed. Water temperature also affects some cell readings — many systems read low in cold water, so check your manual before topping up in spring.

Salt and other water chemistry

Ranges vary by pool surface and equipment; your chlorinator and pool finish manufacturers’ guidance comes first.

Choosing pool salt

Use salt made for pools: at least 99% pure sodium chloride, without anti-caking agents or iodine. Fine-grained salt dissolves faster. Rock salt, water softener pellets with additives and table salt with iodine can cause staining or cloudy water.

What the template pack includes

Printable and Excel pool care logs for salt, chlorine, pH, alkalinity, cyanuric acid and calcium, a salt dosing chart for common pool sizes, a weekly maintenance checklist and a seasonal opening and closing checklist.