How much salt for a 20,000 gallon pool?
A 20,000 gallon pool needs about 534 pounds of salt to go from fresh water to 3,200 ppm: 14 bags of 40 lb.
How to work it out
- In short: the salt to add is the rise you want times the weight of the water in your pool.
- Rise: 3,200 − 0 = 3,200 ppm
- 20,000 gal × 8.345 lb per gal × 3,200 ÷ 1,000,000 = 534 lb
- 534 lb ÷ 40 lb per bag = 13.35 → 14 bags
At 20,000 gallons a salt start-up is a quarter of a ton. Most people buy it in one trip and add it over an afternoon — and the bigger the pool, the more it pays to have a good volume figure before you start, because an overshoot takes a lot of water to fix.
Adjust for your project
- Bags
- 14 bags · 40 lb bag
- Salt rise
- 3,200 ppm
- Salt per 1,000 ppm in this pool
- 166.91 lb (2,671 oz)
- Add pool-grade salt (high-purity sodium chloride, no anti-caking agents or iodine), spread it over the shallow end with the pump running, and brush it until it dissolves. Follow your cell’s manual for start-up and for how long to wait before reading salt.
- Salt never evaporates; it leaves only with water (splash-out, backwash, rain overflow). Liquid chlorine and bleach add about 1.65 ppm of salt per ppm of chlorine used, so overshooting is easy and undoing it means draining.
Fresh water to 3,200 ppm, by pool size
| Pool | Salt to add | Bags |
|---|---|---|
| 10,000 gal | 267 lb | 7 bags |
| 15,000 gal | 401 lb | 11 bags |
| 20,000 gal | 534 lb | 14 bags |
| 25,000 gal | 668 lb | 17 bags |
| 30,000 gal | 801 lb | 21 bags |
| 40,000 gal | 1,068 lb | 27 bags |
Starting up a 20,000 gallon salt pool
Each 1,000 ppm here is about 167 lb of salt. From fresh water to 3,200 ppm is about 534 lb — thirteen and a half 40 lb bags, so fourteen with part of one left over. To Pentair’s 3,600 ppm ideal it is about 601 lb — fifteen bags leaves you a pound short, well within any cell’s range.
- Check the volume first. If the pool really holds 18,000 gallons, fourteen bags puts salt near 3,560 ppm — still in range for most cells, but it shows how volume errors carry through. A 16 × 32 ft diving pool is worked out on how many gallons in a 16x32 inground pool.
- Add in two rounds. Put in about ten bags, run the pump for the time your manual says, test, then add the rest.
- Top-ups. A 300 ppm drop after a rainy season and a few backwashes is about 50 lb — a bag and a quarter.
- Too much? Bringing 4,000 ppm down to 3,200 ppm means replacing about 20% of the water, around 4,000 gallons.
Smaller pools: how much salt for a 15,000 gallon pool and how much salt for a 10,000 gallon pool. The salt cell makes chlorine, but the daily equivalent in liquid chlorine is on how much chlorine for a 20,000 gallon pool.
Different size? Use the full Pool Salt Calculator.
What you’ll need
- Pool salt (40 lb bags)Budget price
High-purity sodium chloride made for salt chlorine generators. Avoid salt with anti-caking agents or iodine.
See options on Amazon (opens in a new tab) - Salt test stripsBudget price
Check salt independently of the salt cell’s own reading, which drifts as the cell ages.
See options on Amazon (opens in a new tab) - Hose water flow meterBudget price
Screws onto the hose and counts gallons, so you know exactly how much went in — and your real fill rate.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much salt for a 20,000 gallon pool at 3,600 ppm?
About 601 pounds, 16 bags of 40 lb, from fresh water.
How much salt to raise a 20,000 gallon pool from 2,800 to 3,200 ppm?
About 67 pounds (2 bags of 40 lb).
Other common sizes
Sources
- Hayward — AquaRite salt chlorination owner’s manual (092538 Rev D) (opens in a new tab) — “The ideal salt level is between 2700-3400 ppm … with 3200 ppm being optimal”; salt usually comes in 40–80 lb bags.
- Hayward — AquaRite S3 manual (1011728 Rev B) (opens in a new tab) — Operating range 1,200–8,000 ppm with 3,200 ppm optimal; default low/high salt alarms at 2,700 and 3,400 ppm.
- Pentair — IntelliChlor Plus / LT owner’s manual (opens in a new tab) — Ideal 3,600 ppm, 2,600–4,500 ppm range; from 0 ppm, 300 lb (136 kg) of salt per 10,000 gallons reaches 3,600 ppm.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- OxyChem — Soda Bleach Solutions Handbook (re-hosted copy) (opens in a new tab) — Trade percent = grams per litre of available chlorine ÷ 10; weight % NaOCl ≈ 1.05 × weight % available chlorine; strength and specific gravity table.