Saltwater Conversion: Salt to Convert Your Pool
Switching a chlorine pool to a salt system? This tool gives the pounds of salt needed to bring a fresh pool up to saltwater salinity, starting from about zero ppm.
Calculator
Converting a fresh 15,000-gallon pool to salt at 3,200 ppm takes 400.3 lb of salt.
Converting an existing chlorine pool to a salt-chlorine system does not change the plumbing or the shell — you install a salt cell and control board on the return line and then dissolve enough salt in the water for the cell to generate chlorine. This tool answers the one number that trips people up: how much salt to buy for the initial dose.
A pool that has run on liquid chlorine, cal-hypo or dichlor usually starts near 0 ppm of salt, so the conversion dose is simply the full weight needed to reach the target from scratch. (If your test shows the water already holds some salt from stabilized chlorine products, use the Salt Calculator and enter that current ppm instead.)
Formula
Starting from roughly zero, the conversion dose is the target concentration times the volume times the solute constant:
salt (lb) = gallons × target ppm × 0.00000834
- gallons — the pool volume you are converting.
- target ppm — the salinity your new cell wants (commonly ~3,200 ppm).
- 0.00000834 — 8.34 lb per US gallon of water ÷ 1,000,000.
This is the Salt Calculator with the current salinity set to zero — the full charge for a fresh pool.
Worked example
Convert a 15,000-gallon pool to 3,200 ppm:
15,000 × 3,200 × 0.00000834 = 400.3 lb
That is about ten 40-lb bags. Add roughly three-quarters first, run the pump for a full day with the generator off, then test and top up. Only switch the cell on once the salt has completely dissolved and the reading is in range.
Planning a salt conversion
Before the salt goes in, get the rest of the water balanced: free chlorine at a normal level, pH around 7.4–7.6, total alkalinity in range, and — importantly for salt pools — cyanuric acid (stabilizer) present so the sun does not burn off the chlorine the cell works hard to make. Balanced water lets the new cell run at a lower output and last longer.
Add salt across the deep end with the pump running and the generator switched off. Give it a full turnover — usually 24 hours — to dissolve completely, brushing any mounds off the floor so they do not stain a vinyl or fiberglass surface. Then verify the salinity with a manual test, not just the cell display, and only start generating once you are inside the manufacturer band.
After the conversion, salt is only lost with water that leaves the pool, so the big initial dose is a one-time purchase. Expect only modest seasonal top-ups thereafter. Keep the cell clean and check the salinity a couple of times a season, and a converted pool is about as low-maintenance as pool water chemistry gets.
Size the cell to the pool, not the other way around. A generator rated for far fewer gallons than you have will run at maximum output for long hours and wear out early, while an oversized cell loafs along and lasts longer. The salt dose, though, does not change with the cell you pick — it depends only on the water volume and the target salinity, which is exactly what this tool computes. So decide your gallons first (use the Pool Volume calculator if you are unsure), choose a cell rated at or above that number, and then buy salt to the pound figure above. Keep the leftover part of the last bag: the first re-test after a full turnover almost always calls for a small top-up.
Frequently asked questions
How much salt to convert a 20,000-gallon pool?
To bring a fresh 20,000-gallon pool to 3,200 ppm you need about 534 lb of salt (20,000 × 3,200 × 0.00000834 = 533.8 lb), roughly thirteen or fourteen 40-lb bags. Add most of it, let it dissolve over a full turnover, then test and finish.
Do I need to drain the pool to convert it to salt?
No. Conversion is additive — you install the cell and dissolve salt into the existing water. You only drain if the water is old, very hard, or high in cyanuric acid, in which case a partial fresh fill first makes the new system easier to balance.
What salinity should I target when converting?
Match the range printed on your salt cell, commonly around 3,200 ppm (often within a 2,700–3,400 ppm window). Undershoot slightly and add more rather than overshoot, since lowering salt means draining and refilling.
My water already has some salt — does that change the dose?
Yes. Stabilized chlorine and some balancing products leave residual salt behind. If a test shows the pool is not at zero, use the Salt Calculator and enter the measured current ppm so you only add the remaining gap.
Is converting to salt cheaper than chlorine?
The salt itself is inexpensive and the initial charge is a one-time buy, but the cell and control board are the up-front cost, and cells wear out over several seasons. This tool sizes only the salt; it stores no prices, so plug in your own equipment costs to compare.