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Pool Salt Calculator

This pool salt calculator tells you exactly how much salt to add to a saltwater pool. Enter your gallons, the salinity your test strip shows now, and the level your chlorine generator wants. You get pounds of salt and a bag count so you can buy the right amount on the first trip.

Pool salt calculator illustration of a bag of pool salt pouring into saltwater pool water beside a chlorine generator

Run the numbers

Formula used

Pounds of Salt = Gallons x 8.34 x (Target ppm - Current ppm) / 1,000,000

Your result

Salt to add
233.5 lbs
Bags to buy
6 bags
In kilograms
105.9 kg
Salinity increase
1,400 ppm

Results update as you type. Round up when you buy materials.

How the pool salt calculator works

Salt is measured in parts per million. One ppm means one pound of salt for every million pounds of water, and a gallon of water weighs 8.34 pounds.

The tool also warns you when your current level is already above target, since the only way down is to drain water and refill.

The formula, step by step

Pounds of Salt = Gallons x 8.34 x (Target ppm - Current ppm) / 1,000,000

  • Subtract your current salinity from the target salinity.
  • Multiply pool gallons by 8.34 to get the weight of the water.
  • Multiply that weight by the ppm gap, then divide by one million.
  • Divide the pounds by 40 to get the number of standard bags.

Worked example

A 20,000 gallon pool tests at 1,800 ppm and the generator wants 3,200 ppm.

Gap = 1,400 ppm. Water weight = 20,000 x 8.34 = 166,800 pounds.

Salt needed = 166,800 x 1,400 / 1,000,000 = 233 pounds, which is six 40 pound bags.

Watch it done

This short video walks through the same job in real life, so you can match what you see on screen to what you do at the pool.

Video guide: How Much Salt to Add to a Salt Water Pool by Swim University. Video hosted on YouTube.

Tips before you start

Pour salt into the shallow end with the pump running and brush it toward the main drain. Leave the generator off for 24 hours while the salt dissolves so the cell reads a true level.

Buy salt labeled for pool use, at least 99 percent pure sodium chloride, with no anti caking agents or iodine. Water softener pellets take far longer to dissolve and can stain a plaster finish.

Pool Salt Calculator FAQs

How much salt does a 20,000 gallon pool need?

Going from zero to 3,200 ppm takes about 534 pounds, or fourteen 40 pound bags. If salt is already in the water, only the gap matters.

What salt level should a saltwater pool run at?

Most chlorine generators want 2,700 to 3,400 ppm, with 3,200 ppm as a common target. Check the sticker on your cell.

How do I lower salt that is too high?

Drain part of the pool and refill with fresh water. Salt does not evaporate, so dilution is the only fix.

How often do I add salt?

Salt only leaves through splash out, backwashing, leaks and rain overflow. Most pools need a top up once or twice a season.