Pool Salt Calculator
Pool volume and current salt reading in — pounds and 40 lb bags of salt out, sized to your generator's target.
The short answer
Formula. Pounds of salt = pool gallons × 8.345 × (target ppm − current ppm) ÷ 1,000,000.
Example. Taking a fresh 10,000-gallon pool to 3,200 ppm needs about 267 lb of salt — seven 40-lb bags.
How this calculator works
Salinity in ppm (parts per million) is a weight-of-salt-per-weight-of-water ratio, so the math is just proportion. One US gallon of water weighs about 8.345 lb, so 10,000 gallons of pool water is roughly 83,450 lb. To raise salinity by 1 ppm you add one millionth of that water's weight in salt — about 0.083 lb per 1,000 gallons. Raising 10,000 gallons from 2,500 to 3,200 ppm is a 700 ppm rise: 700 × 0.0835 ≈ 58 lb, a bag and a half of 40 lb pool salt.
The same proportion runs in reverse for a fresh fill: from 0 to 3,200 ppm in 10,000 gallons is 3,200 × 0.0835 ≈ 267 lb, seven 40 lb bags. The calculator derives your pool's gallons from dimensions if you do not know them — length × width × average depth × 7.48 for a rectangle (a 16 × 32 × 5 ft pool is about 19,150 gallons), or diameter² × average depth × 5.9 for a round one. Average depth is the shallow and deep end depths averaged; for very uneven bottoms that estimate is only as good as your honesty about the deep end.
Practical technique matters more than the third decimal. Add salt in batches of about 80% of the calculated amount, pour it into the deep end with the pump running, brush any piles off the liner, wait a full circulation cycle, then re-test before adding the rest — salt test strips and even cell displays lag reality until the water fully mixes. Never let the "add salt" arithmetic bully you past your system's maximum: too much salt cannot be removed except by draining and refilling, while too little is a cheap bag away from fixed.
Sources & review date
- Pool water weighs 8.345 lb per gallon — the constant all pool-dosing math rests on.
- Target range 3,000–3,400 ppm is the salt-chlorinator industry standard; confirm against your unit's manual.
Last reviewed: October 2026. Numbers that drift (fees, prices, densities) are editable inputs on this page.
Pool salt FAQs
What kind of salt should I use in a pool?
Pure sodium chloride labeled for pools — usually 99%+ fine solar or mechanically evaporated salt. Avoid anything with anti-caking additives or iodine (table salt), which cloud water and stain over time. "Pool salt" and water-softener salt pellets of the right purity both work; the label matters more than the bag.
How long after adding salt can I swim?
Once the salt is fully dissolved — typically 15–30 minutes of pump circulation after brushing the piles. Salt itself is not a hazard at pool concentrations; the reason to wait is unmixed concentration pockets and seeing the bottom.
Why does my generator still say low salt after adding the calculated amount?
Almost always incomplete mixing, a dirty cell, or cold water — all three make the cell read low before the water is truly low. Circulate a few hours, clean the cell if due, re-test with strips or a drop kit, and only then top up with the calculator again.
Does rain or splash-out lower my salt level?
Rain dilutes salt down; splash-out and backwashing carry salt away with the water. After a heavy week of either, re-test — topping back up is the same calculation with your new current reading.