Pool Salt Calculator
Enter your pool's gallons, the current salt reading and your generator's target. You get the pounds and 40 lb bags to add, how much each bag moves the reading, and how much to drain if you overshot.
Use the pool volume calculator if unsure.
From a test strip, meter, or the generator's reading. 0 for a fresh fill.
Check your generator's manual: most want 2,700-3,400; 3,200 is typical.
Salt to add
133 lb
to go from 2,400 to 3,200 ppm
40 lb bags
3.3
buy 4, add 3 first and retest
Each 40 lb bag adds
240 ppm
in 20,000 gal
Water to drain if over
—
reading is at or under target
lb = (target − current) ppm × gallons × 8.34 ÷ 1,000,000. Add salt across the shallow end with the pump running and the generator off, brush it in, and wait 24 hours before retesting; readings drift as it dissolves.
Pounds of salt to reach 3,200 ppm
| Pool | from 0 ppm | from 1,000 ppm | from 2,000 ppm | from 2,500 ppm | from 2,800 ppm | ppm per 40 lb bag |
|---|---|---|---|---|---|---|
| 10,000 gal | 267 lb (6.7 bags) | 183 lb (4.6 bags) | 100 lb (2.5 bags) | 58 lb (1.5 bags) | 33 lb (0.8 bags) | 480 |
| 12,000 gal | 320 lb (8.0 bags) | 220 lb (5.5 bags) | 120 lb (3.0 bags) | 70 lb (1.8 bags) | 40 lb (1.0 bags) | 400 |
| 15,000 gal | 400 lb (10.0 bags) | 275 lb (6.9 bags) | 150 lb (3.8 bags) | 88 lb (2.2 bags) | 50 lb (1.3 bags) | 320 |
| 18,000 gal | 480 lb (12.0 bags) | 330 lb (8.3 bags) | 180 lb (4.5 bags) | 105 lb (2.6 bags) | 60 lb (1.5 bags) | 266 |
| 20,000 gal | 534 lb (13.3 bags) | 367 lb (9.2 bags) | 200 lb (5.0 bags) | 117 lb (2.9 bags) | 67 lb (1.7 bags) | 240 |
| 25,000 gal | 667 lb (16.7 bags) | 459 lb (11.5 bags) | 250 lb (6.3 bags) | 146 lb (3.6 bags) | 83 lb (2.1 bags) | 192 |
| 30,000 gal | 801 lb (20.0 bags) | 550 lb (13.8 bags) | 300 lb (7.5 bags) | 175 lb (4.4 bags) | 100 lb (2.5 bags) | 160 |
| 40,000 gal | 1068 lb (26.7 bags) | 734 lb (18.3 bags) | 400 lb (10.0 bags) | 234 lb (5.8 bags) | 133 lb (3.3 bags) | 120 |
How to add it
- Test first with an independent method; do not trust the cell display alone.
- Turn the chlorine generator off (or to 0%) so undissolved salt does not hit the cell; leave the pump running.
- Add about three-quarters of the calculated amount, spread around the shallow end, and brush it toward the main drain.
- Run the pump 24 hours, retest, and add the remainder if needed. Under-shooting is cheap to fix; over-shooting means draining water.
- Turn the generator back on and check its reading against the test.
Why salt only goes down slowly
Salt is not consumed by the chlorine generator: the cell splits it into chlorine and it recombines back into salt after sanitising. The only losses are splash-out, backwashing, rain overflow and draining. That is why a salt pool needs a few bags a season, not a bag a week, and why a reading that keeps dropping points to a leak or heavy backwashing rather than the cell.
Frequently Asked Questions
How much salt do I add to my pool?
(Target ppm − current ppm) × gallons × 8.34 ÷ 1,000,000 pounds. A 20,000-gallon pool at 2,400 ppm going to 3,200 needs 133 lb, about 3.3 40 lb bags. A fresh 20,000-gallon fill at 0 ppm needs 534 lb, or 14 bags.
What salt level should a pool be?
Whatever the salt chlorine generator's manual says: most Hayward, Pentair and Jandy cells want 2,700 to 3,400 ppm with 3,200 as the target; some newer cells run at 3,000 to 4,000 and a few low-salt models at 1,500. The calculator's target box takes any figure. Too low and the cell stops producing chlorine; too high and it throws a high-salt fault and the water tastes salty.
How many bags of salt for a 15,000 gallon pool?
From zero to 3,200 ppm: 400 lb, so 11 bags of 40 lb. From 2,500 ppm: 88 lb, or 3 bags. Each 40 lb bag adds about 320 ppm in 15,000 gallons.
What kind of salt?
Pool salt, water-softener salt or food-grade salt that is at least 99% pure sodium chloride with no additives: no iodine, no anti-caking agents, no rust inhibitors. Pool salt is simply fine-ground pure salt that dissolves quickly. Rock salt for ice melting is not pure enough.
Why does my salt reading disagree with the generator?
Cells estimate salt from conductivity, which depends on temperature; cold water reads low. Test strips are ±200 ppm at best. A pool store's meter or a K-1766 drop test is the reference. Add salt to the independent test, not to the cell's display, and give the water 24 hours to mix before deciding the reading is wrong.
These calculators use published seeding rates, extension-service fertilizer guidance, and standard pool-chemistry dosing figures, and are for planning. Read the product label; it governs the dose. Pool chemicals are hazardous when mixed or mishandled, and a pool store's water test beats any estimate here.