How to use the pool salt calculator
Enter the pool’s volume in gallons (the pool volume calculator works it out from the size), your current salt reading (0 for a fresh fill) and the target from your chlorinator’s manual. Use a test strip or digital meter for the reading — the generator’s own display can drift.
The formula
Pounds of salt = gallons × 8.34 × (target ppm − current ppm) ÷ 1,000,000
8.34 is the weight of a gallon of water in pounds; ppm means pounds of salt per million pounds of water.
Worked example: new 20,000 gallon pool
- 20,000 × 8.34 × 3,200 ÷ 1,000,000 = 534 lb
- 534 ÷ 40 = 13.3 → 14 bags of 40 lb
Add salt in stages if you’re unsure of the volume: add about three-quarters, let it dissolve, test, then top up. It’s easy to add more and hard to take it out.
Salt to reach 3,200 ppm by pool size
Pounds of salt to add. For bags, divide by the bag weight and round up — the calculator does this for you.
| Pool volume | New fill (0 ppm) | From 2,500 ppm | From 2,700 ppm |
|---|---|---|---|
| 5,000 gal | 133 lb | 29 lb | 21 lb |
| 10,000 gal | 267 lb | 58 lb | 42 lb |
| 15,000 gal | 400 lb | 88 lb | 63 lb |
| 18,000 gal | 480 lb | 105 lb | 75 lb |
| 20,000 gal | 534 lb | 117 lb | 83 lb |
| 25,000 gal | 667 lb | 146 lb | 104 lb |
| 30,000 gal | 801 lb | 175 lb | 125 lb |
| 40,000 gal | 1,068 lb | 234 lb | 167 lb |
Common mistakes
- Guessing the pool’s volume. A wrong gallon figure throws off every pound; work it out from the pool’s size.
- Trusting the generator’s salt display. It can drift — test with a strip or a digital meter first.
- Running the generator before the salt dissolves. Brush it around, run the pump and wait.
- Adding it all at once when unsure. Add most of it, test, then top up; too much salt means draining water.
Frequently asked questions
How much salt does a 20,000 gallon pool need?
About 534 lb — 14 bags of 40 lb — to go from 0 to 3,200 ppm. If the water already has salt, enter the current reading to add only the difference.
What salt level should a saltwater pool have?
Most chlorine generators run between 2,700 and 3,400 ppm, ideally around 3,200 ppm. Your generator's manual has the exact range.
How do I lower the salt level?
Salt doesn't evaporate, so the only way down is to drain part of the water and refill with fresh water. To go from 4,000 to 3,200 ppm, replace about 20%.
How long after adding salt can I swim?
Brush the salt around and run the pump; it dissolves within about 24 hours. Wait for it to dissolve before turning the generator back on.
How many bags of salt for a 10,000 gallon pool?
About 267 lb — 7 bags of 40 lb — to go from 0 to 3,200 ppm on a new fill.
How much salt raises the level by 500 ppm?
About 42 lb per 10,000 gallons. For a 20,000 gallon pool going from 2,700 to 3,200 ppm, that's 83 lb.
How much salt for a 40,000 gallon pool?
About 1,068 lb — 27 bags of 40 lb — from 0 to 3,200 ppm.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.