Pool Salt Calculator

What this pool salt calculator does

This calculator works out the pounds of pool salt you need to dissolve into your pool to bring its salinity (in parts per million, ppm) from where it is now to the target your saltwater chlorinator (SWG) wants. Most SWGs sit in the 3,000–3,500 ppm band — the calculator defaults to 3,200 ppm, which is the safest single target across Hayward, Pentair, Jandy and CircuPool models. The output is the pounds of salt to add plus the 40 lb bag count and a typical price range so you can plan the home-centre run.

How to use the pool salt calculator

1. Paste your pool volume in gallons. If you don’t know it, head to the Pool Volume Calculator first — the salt dose changes by ~17 lb per 1,000 gallon error, so accuracy matters.
2. Enter the current salinity in ppm. For a fresh fill from municipal water it’s effectively 0 (some municipal supplies read 100–200 ppm from naturally dissolved minerals — close enough). For an existing pool, use a test-strip or digital-meter reading.
3. Enter the target salinity. 3,200 ppm is the default; check your SWG’s manual if your unit calls for a different number.
4. Read the result. The headline pounds figure is what you need; the bag count and price help size the trip to the store.
5. Tap Copy summary to text it to your service or paste it into a pool-care log.

How the formula works

Salt dosing uses one of the simplest pieces of pool chemistry:

lb of salt = (target_ppm − current_ppm) × gallons × 8.345 ÷ 1,000,000

The 8.345 is the weight in pounds of one US gallon of water. ppm literally means “parts per million by mass,” so to add 1 ppm to one million pounds of water you add one pound of solute. The formula just scales that down to your pool’s gallons. For metric users the equivalent is (target_ppm − current_ppm) × litres ÷ 1,000,000 kilograms — and 1 kg = 2.2046 lb.

Salt-chlorinator targets at a glance

These are the manufacturer-published targets. Stay within ±200 ppm of them — going too high doesn’t make the cell produce more chlorine, it just corrodes ladders and rails, and over ~4,500 ppm you start to taste it.

Picking the right salt bag

Look for “99.8 % pure pool salt” or “food-grade NaCl” on the bag. Morton Pool Salt, Diamond Crystal Pool Salt, and Aquasalt are the three most common US retail brands. Avoid:

• Water-softener pellets unless the bag says “no additives” — many brands include YPS (yellow prussiate of soda) anti-caker that stains pool plaster.
• Iodised table salt — the iodine reacts with chlorine and turns pool water pink-grey.
• Rock salt — coarse, dirty, won’t dissolve fast enough, often has iron-staining impurities.
• Road de-icer salt — calcium chloride, which raises water hardness and damages the SWG cell.

How to actually add the salt

The most-violated rule on the pool deck: broadcast the salt across the deep end with the pump running. Do not dump it into the skimmer. Skimmer dumping pushes a slug of saturated salt water through the salt cell and the heater’s copper heat exchanger, which can damage both within minutes. Broadcast across the surface and let the pool’s circulation dissolve it; brush any settled salt off the floor toward the main drain so it doesn’t sit on plaster or vinyl. Keep the pump running for 24 hours before re-testing and switching the SWG on.

When to add vs. drain and refill

If your salt level is above target (over-added on the last dose, or evaporation concentrated the salt), the only way down is to partial-drain and refill with fresh water. Use the salt formula in reverse: to drop 20,000 gal from 4,500 ppm to 3,200 ppm you need to replace about 29 % of the water with fresh. Salt does not evaporate — only water does, so heavy summer evaporation slowly concentrates the salt. Heavy rain or backwash drops it. Test monthly.

Privacy

This calculator runs in JavaScript on your device. There is no fetch call, no analytics on the values you enter, no server-side logging. The page works the same way offline once loaded.