Pool Salt Calculator
Find out exactly how many pounds of salt to add for your salt water chlorine generator. Works for startups from fresh water and for topping up after rain or splash-out.
Use pool-grade salt (99%+ pure sodium chloride) with no additives. Add half the calculated amount, let it circulate 24 hours, retest, then add the rest as needed.
How the salt dose is calculated
Parts per million is a weight ratio: 1 ppm of salt means 1 pound of salt per million pounds of water. A gallon of water weighs 8.34 pounds, which gives a simple exact formula:
There is no approximation here, unlike chemical dosing, salt math is exact. The only uncertainty is your volume figure, so if you have never calculated it properly, run your dimensions through the pool volume calculator first.
Worked example: fresh start at 15,000 gallons
- Target: 3,200 ppm. Current: 0 ppm (fresh fill). Difference: 3,200 ppm.
- 3,200 x 15,000 x 8.34 = 400,320,000
- Divide by 1,000,000: about 400 lbs of salt
- At 40 lbs per bag: 10 bags
Salt costs roughly $6 to $10 per 40 lb bag at big-box stores, so a full startup on a 15,000 gallon pool runs $60 to $100. After that, salt only leaves through backwash, splash-out, and overflow, an annual top-up of 1 to 3 bags is typical.
How to add salt the right way
- Test your current level twice (test strips vary) and average the readings.
- Turn the salt generator OFF but leave the pump running.
- Pour half the calculated salt slowly around the shallow end perimeter, brushing any piles toward the main drain.
- Circulate 24 hours, retest, then add the remainder as needed.
Adding in halves matters because test kits and volume estimates both carry error, and removing salt requires draining water. Sneak up on the target from below.
Salt reference table (target 3,200 ppm from fresh water)
- 10,000 gallons: about 267 lbs (7 bags)
- 15,000 gallons: about 400 lbs (10 bags)
- 20,000 gallons: about 534 lbs (13.5 bags)
- 25,000 gallons: about 667 lbs (17 bags)
- 30,000 gallons: about 800 lbs (20 bags)
Frequently asked questions
How much salt does a 15,000 gallon pool need?
Starting from zero, a 15,000 gallon pool needs about 400 lbs of salt (ten 40 lb bags) to reach 3,200 ppm. From a typical partial level of 1,000 ppm, it needs about 275 lbs to top up to 3,200 ppm.
What salt level should my pool be?
Most salt water generators run best between 2,700 and 3,400 ppm, with 3,200 ppm the most common target. Check your specific cell's manual: some Pentair and Hayward models specify different ideal ranges, and running too low damages the cell.
What kind of salt should I use?
Pool-grade sodium chloride that is at least 99 percent pure, with no iodine, no anti-caking agents (yellow prussiate of soda), and no rust inhibitors. Water softener pellets of equivalent purity dissolve slower but work. Never use rock salt or ice-melt products.
My salt level is too high. How do I lower it?
Salt does not evaporate or degrade; the only way to lower it is dilution. Partially drain the pool and refill with fresh water. To go from 4,000 to 3,200 ppm you need to replace about 20 percent of the water.
How long after adding salt can I turn on the salt generator?
Wait until the salt fully dissolves and circulates, typically 24 hours with the pump running. Running the cell while undissolved salt drifts across it can damage the plates and gives false readings.