Pool Salt Calculator

Saltwater pools need a precise salt concentration to keep the chlorine generator producing and the water comfortable. Enter your pool dimensions, current ppm reading, and target — we'll tell you exactly how many pounds of pool salt to add and how many 40 lb bags to pick up at the store.

How Saltwater Pools Work

A saltwater pool isn't chlorine-free — it generates its own chlorine on demand from dissolved salt using an electrolytic chlorine generator (a.k.a. salt cell). The cell needs the right salt concentration to operate, typically 3,000–3,400 ppm. Below that, the generator under-produces chlorine and usually flashes an error light. Above 3,500 ppm there's no chlorine benefit, just creeping corrosion risk on metal pool components.

How to Calculate Salt Needed

The math: lbs of salt = gallons × (target − current ppm) × 0.00000835. A 20,000-gallon pool needing to climb from 2,800 to 3,200 ppm needs roughly 67 lbs of salt — about two 40-lb bags. Always under-dose slightly, run the pump for 24 hours to fully circulate, retest, and top up. Overshooting is much harder to undo than topping up later.

How This Calculator Works

A saltwater pool needs a target salinity, usually around 3,200 ppm, and the dose depends on how far below target you are and how much water you have. The calculator first estimates volume in gallons from the pool's shape: rectangle is length × width × average depth × 7.48 (gallons per cubic foot); an oval uses a 5.9 factor; a round pool uses π × radius² × depth × 7.48.

Then it finds the gap, target ppm minus current ppm, and never goes negative. The pounds of salt are gallons × ppm gap × 0.00000835, the conversion factor for raising salinity by parts per million in U.S. gallons. That total is divided by 40 and rounded up to give 40-lb bags. If your current reading already meets the target, the dose is zero — you never want to overshoot, because the only fix for too much salt is draining and refilling.

A Worked Example

A 16×32 ft rectangular pool averaging 5 ft deep, reading 2,400 ppm now, targeting 3,200 ppm. Volume: 16 × 32 × 5 × 7.48 = 19,149 gallons. The gap is 3,200 − 2,400 = 800 ppm. Salt: 19,149 × 800 × 0.00000835 = about 127.9 lbs. Divide by 40 and round up = 4 bags. Pour it in over the deep end with the pump running, brush to dissolve, and re-test in 24 hours before adding more.

Estimator's tip: Add salt in stages, not all at once. Pour in about three-quarters of what the calculator shows, run the pump 24 hours with the cell off until it fully dissolves, then re-test and top up. It is far easier to add another bag than to drain and refill an overshot pool. Brush any salt that piles on the floor, and never run the chlorine generator until the reading stabilizes in your unit's range.

What Affects Your Salt Needed

• Your current salinity reading — test before dosing, since the gap drives everything.
• Pool volume, which depends on accurate average depth, not just the deep end.
• Target set by your salt chlorine generator (commonly 2,700–3,400 ppm; check the manual).
• Rain, splash-out, and backwashing that dilute salt over a season.
• Salt purity — use pool-grade (99%+) salt; water-softener or rock salt adds impurities.
• Water temperature, which slows how fast salt dissolves but not how much you need.

Frequently Asked Questions

How much salt do I need for my saltwater pool?

Multiply your pool's gallons by the ppm increase you need by 0.00000835 to get pounds, then divide by 40 for bags. A 20,000-gallon pool raising 800 ppm needs about 134 pounds, or four 40-pound bags.

What salt level should a saltwater pool be?

Most salt chlorine generators target 2,700 to 3,400 ppm, with 3,200 ppm a common sweet spot. Always follow your specific generator's manual, since running too low or too high can damage the cell.

What kind of salt do I add to a pool?

Use pool-grade sodium chloride that is at least 99% pure, sold as pool salt. Avoid rock salt, water-softener pellets with additives, and anything with anti-caking or iron, which can stain.

What if my pool already has enough salt?

Then you add nothing. The calculator returns zero when your current reading meets the target. Overshooting can only be corrected by partially draining and refilling, so always dose conservatively and re-test.