Enter your pool volume, the salt level you have now and the level your salt chlorine generator wants. The calculator gives the pounds of pool salt to add and the number of 40 lb bags to buy.
How to use the pool salt calculator
- Enter the volume of the pool in US gallons. If you do not know it, work it out first with the pool volume calculator.
- Test the water and enter the current salt level in ppm. Use 0 for a new pool or after a refill.
- Enter the target from your chlorinator manual. Hayward recommends about 3,200 ppm for its Aqua Rite systems.
- Add salt a little below the full amount, run the pump for 24 hours, then retest before adding the rest.
Pool salt formula
Salt (lb) = (target ppm − current ppm) × gallons × 8.34 ÷ 1,000,000 Bags = salt (lb) ÷ bag size, rounded up Water to replace if too salty = (current − target) ÷ current
One part per million is one pound of salt in a million pounds of water. A US gallon holds 231 cubic inches (NIST), and water weighs about 62.4 lb per cubic foot (USGS), so a gallon of water weighs about 8.34 lb.
Worked example: a new 15,000 gallon pool
- Salt to raise: 3,200 − 0 = 3,200 ppm.
- Salt: 3,200 × 15,000 × 8.34 ÷ 1,000,000 = 400.3 lb.
- Bags of 40 lb: 400.3 ÷ 40 = 10.01, so buy 11 bags; ten bags leaves you about 0.3 lb short, which is still inside Hayward’s range.
Topping up the same pool from 2,600 ppm to 3,200 ppm takes 600 × 15,000 × 8.34 ÷ 1,000,000 = 75 lb, or two bags.
Pounds of salt for 3,200 ppm from fresh water
| Pool size | Salt needed | 40 lb bags | To raise 100 ppm |
|---|---|---|---|
| 5,000 gal | 133 lb | 4 | 4.2 lb |
| 10,000 gal | 267 lb | 7 | 8.3 lb |
| 15,000 gal | 400 lb | 11 | 12.5 lb |
| 20,000 gal | 534 lb | 14 | 16.7 lb |
| 25,000 gal | 667 lb | 17 | 20.9 lb |
| 30,000 gal | 801 lb | 21 | 25 lb |
What salt level does a salt pool need?
It depends on the cell. Hayward says its Aqua Rite system works best at about 3,200 ppm and will run anywhere from 2,700 to 3,400 ppm, which it compares to about a teaspoon of salt per gallon. Other brands use different targets, so always check the manual for your chlorine generator and enter that number as the target.
What if the salt level is too high?
Salt does not evaporate or get used up by the chlorinator, so the only way to lower it is to replace water. Draining a share of the water and refilling with fresh water lowers the salt by the same share: going from 4,000 to 3,200 ppm means replacing about 20% of the water. Salt is lost slowly through splash-out, backwashing and rain overflow, which is why most pools need a top-up each season.
Tips for adding pool salt
- Use pool salt. Buy salt sold for pools or chlorine generators, not rock salt with additives.
- Spread it around the deep end. Pour salt into the pool with the pump running and brush it until it dissolves.
- Turn the cell off while salt dissolves if your manual says to, then retest after 24 hours.
- Add in steps. Adding a little less than the full amount and retesting is easier than draining water later.
Questions
How much salt do I need for a 10,000 gallon pool?
About 267 lb, or seven 40 lb bags, to bring fresh water to 3,200 ppm. Raising an existing pool by 100 ppm takes about 8.3 lb.
How many bags of salt for a 20,000 gallon pool?
Fourteen 40 lb bags, about 534 lb, take fresh water to 3,200 ppm.
How much does 40 lb of salt raise the ppm?
In 10,000 gallons, a 40 lb bag raises the salt by about 480 ppm. In 20,000 gallons it raises it by about 240 ppm.
Can I add too much salt to my pool?
Yes. If the reading is above your chlorinator’s range, the only fix is to drain part of the water and refill with fresh water.
Sources
- How much salt does the system require?, Hayward.
Used for: Aqua Rite works best at about 3,200 ppm and operates from 2,700 to 3,400 ppm; about a teaspoon per gallon. - Water Density, U.S. Geological Survey Water Science School.
Used for: Water weighs about 62.4 lb per cubic foot, used for the weight of a gallon. - NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: US gallon = 231 in³; pound to kilogram conversion.