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Reviewed · Prices checked October 2026 · How we calculate

Pool Salt Calculator: How Many 40 lb Bags

Enter your pool's gallons and the salt level you have now and want. You get the pounds of salt and the 40 lb bags to buy, and what they cost at your store's price.

Pool and salt level

Units
gal

Gallons of water in the pool. Don't know your gallons? Use the pool volume calculator.

ppm

Use test strips or your generator's display. A new fill is 0.

ppm

Check your generator's manual. Most want 2,700–3,400 ppm.

Shopping list

Updates as you type
13bags

of 40 lb pool salt (520 lb) to take 18,000 gal from 0 ppm to 3,200 ppm

You need 480.4 lb of salt, so 13 bags.

  • 13 bags of pool salt (40 lb each)$91–$325
    480.4 lb needed ÷ 40 lb = 12.01 bags, rounded up. About 39.6 lb left over for top-ups.

    Typical price (estimate, checked Oct 2026): $7.00–$25.00 per 40 lb bag of pool salt

    13 bags × $7.00–$25.00 = $91–$325Estimate
Project total (estimate where no price is entered)$91–$325
Checked Oct 2026
Show the math
Pool volume: 18,000 galSalt to add: 3,200 − 0 = 3,200 ppm18,000 gal × 3,200 ppm × 8.34 lb per gal ÷ 1,000,000 = 480.4 lb480.4 lb ÷ 40 lb per bag = 12.01 → 13 bags

Your prices are saved on this device only. Pool salt is sold in 40 lb bags in the US, so the answer stays in pounds; liters convert to US gallons (1 gal = 3.785 L).

How it works

The formula

pounds of salt = gallons × (target ppm − current ppm) × 8.34 ÷ 1,000,000
bags = pounds ÷ 40, rounded up

A reading of 1 ppm means 1 part salt in a million parts water by weight. A gallon of water weighs 8.34 lb, so every 1,000 ppm in 10,000 gallons takes 83.4 lb of salt.

Assumptions

  • Water weighs 8.34 lb per US gallon. Salt barely changes the volume, so we ignore that.
  • The target is up to you. Most saltwater chlorine generators want 2,700–3,400 ppm, and 3,200 ppm is a common setting. Hayward lists 3,200 ppm for its AquaRite cells, but models differ, so check your generator's manual.
  • Salt comes in 40 lb bags, and you buy whole bags, so the count rounds up. The calculator shows how much is left over for later top-ups.
  • Buy pool-grade salt that is at least 99% pure sodium chloride (check the bag). This page covers salt only, not chlorine, pH or alkalinity.
  • Metric: type liters. They convert to US gallons for the math (3.785 L per gallon), and the salt still comes in 40 lb bags.

Worked example

18,000 gallon pool, new fill: 0 to 3,200 ppm

  1. Salt to add: 3,200 − 0 = 3,200 ppm
  2. Pounds: 18,000 × 3,200 × 8.34 ÷ 1,000,000 = 480.4 lb
  3. Bags: 480.4 ÷ 40 = 12.01, so buy 13 bags
  4. At typical prices ($7.00–$25.00 a bag): $91–$325

Salt for common pool sizes

Pounds of salt and 40 lb bags to reach 3,200 ppm, from a new fill and from 2,500 ppm
Pool sizeFrom 0 ppmFrom 2,500 ppm
PoundsBagsPoundsBags
10,000 gal266.9758.42
15,000 gal400.31187.63
20,000 gal533.814116.83
25,000 gal667.2171464
30,000 gal800.621175.15

Target 3,200 ppm, 40 lb bags, rounded up. Your pool size is not listed? Type it in the calculator above.

Questions people ask

How much salt do I need for a saltwater pool?

For a new 18,000 gallon pool going from 0 to 3,200 ppm, you need 480.4 lb, so 13 bags of 40 lb. Salt is a one-time fill; after that you only top up what you lose.

How much salt per 10,000 gallons?

83.4 lb raises 10,000 gallons by 1,000 ppm. To go from 0 to 3,200 ppm takes 266.9 lb, or 7 bags of 40 lb.

How often do I add salt?

Salt does not burn off. You lose it when water leaves the pool: splash-out, backwashing, heavy rain that overflows, or a partial drain. Test every month or so and at the start of the season, and add salt only when the reading drops below your target. Each time, enter your reading as the current level.

What ppm should my salt level be?

Follow your generator's manual. Most want 2,700–3,400 ppm, and 3,200 ppm is a common target. Too low and the cell makes less chlorine; too high can trigger an error or wear on pool surfaces and equipment.

Can I add too much salt?

Yes, and you cannot take it out. Only dilution lowers it: drain some water and refill with fresh water. For example, at 4,000 ppm in 18,000 gallons, replacing about 3,600 gallons (20%) brings you to 3,200 ppm. Add salt in stages and retest if you are unsure.