How to use
- Enter your pool volume in US gallons, or switch to metric and enter liters. If you don't know it, use the pool volume calculator linked above.
- Test your water and enter the current salt reading in ppm. Use 0 for a new pool.
- Enter the target ppm from your salt cell manual.
- Pick your bag size, or choose "Other size" and enter the weight printed on your bag.
- Select "Calculate". You get the pounds of salt, the number of bags, and the level you'd reach with whole bags.
How the calculation works
Salt level is measured in parts per million (ppm) by weight. That means pounds of salt per million pounds of water. A US gallon of water weighs about 8.34 pounds, so one million pounds of water is about 120,000 gallons.
Pounds of salt = gallons × 8.34 × (target ppm − current ppm) ÷ 1,000,000.
Example: a 20,000 gallon pool reads 2,000 ppm and you want 3,200 ppm. You need to add 1,200 ppm. 20,000 × 8.34 × 1,200 ÷ 1,000,000 = 200.16 pounds. With 40 lb bags that is 5.004 bags, so you round up to 6 bags. Six bags would bring the pool to about 3,439 ppm, and five bags to about 3,199 ppm. Because five bags is almost exactly enough, you may prefer to add five bags and then retest.
For liters, the calculator divides by 3.785411784 to get US gallons first, then applies the same formula.
Salt needed by pool size
Pounds of salt to raise the level by the amount shown, calculated with the formula above. Use it as a quick check on the calculator.
| Pool size (US gallons) | +500 ppm | +1,000 ppm | +2,000 ppm | +3,000 ppm | +3,200 ppm |
|---|---|---|---|---|---|
| 5,000 | 20.9 lb | 41.7 lb | 83.4 lb | 125.1 lb | 133.4 lb |
| 10,000 | 41.7 lb | 83.4 lb | 166.8 lb | 250.2 lb | 266.9 lb |
| 15,000 | 62.6 lb | 125.1 lb | 250.2 lb | 375.3 lb | 400.3 lb |
| 20,000 | 83.4 lb | 166.8 lb | 333.6 lb | 500.4 lb | 533.8 lb |
| 25,000 | 104.3 lb | 208.5 lb | 417.0 lb | 625.5 lb | 667.2 lb |
| 30,000 | 125.1 lb | 250.2 lb | 500.4 lb | 750.6 lb | 800.6 lb |
Every 10,000 gallons needs about 8.3 lb of salt for each 100 ppm. Divide the pounds by your bag size and round up to get bags.
What target should you use?
There is no single number. The right salt level depends on your salt chlorine generator, so look it up in the manual for your model, or on the label of the salt cell. As examples from published manuals, one Hayward SwimPure Plus manual lists 2,700 to 3,400 ppm with 3,200 ppm as optimal. One Pentair IntelliChlor guide lists 3,600 to 4,500 ppm with 3,600 ppm as ideal. These are examples for those models only. Enter the number for your own equipment.
How to add salt
These are general steps. Your manual comes first.
- Test the current salt level before you add anything.
- Use the salt type your manual calls for. One Hayward manual says to use sodium chloride that is more than 99% pure, and not to use salt with additives such as anti-caking agents or iodine.
- Turn the circulation pump on and pour the salt into the pool. Brush it around so it does not pile up on the bottom.
- Run the pump for about 24 hours so the salt spreads evenly. One Hayward manual says the salt reading may take that long to update.
- If the pool was just replastered, check the plaster maker's advice and your manual first. One Hayward manual says to wait 10 to 14 days before adding salt to new plaster.
- Retest before you add more.
If your salt level is too high
Salt does not evaporate, so topping off with water won't lower it. A Hayward manual says the only way to lower the level is to drain part of the pool and refill with fresh water. The share to drain is 1 minus the target divided by the current level. Going from 3,500 ppm to 3,000 ppm means draining about 14.3% of the water. That math assumes the fresh water has almost no salt. Refill water that already has salt in it will leave you higher than the estimate.
Common mistakes
- Using imperial gallons. An imperial gallon is about 20% larger than a US gallon. If your pool was sized in imperial gallons, convert it or enter liters.
- Trusting one test strip. One Pentair guide says its salt sensor reading is within plus or minus 500 ppm. That is a lot when you are adding salt. Retest with a second method if the number looks off.
- Retesting too soon. Salt takes time to dissolve and spread. If you test right after adding it, the reading can be low or uneven. Circulate the water first.
- Guessing the volume. A pool that is 3,000 gallons larger than you think ends up with a lower salt level than you wanted. Measure the pool first.
- Using the wrong target. A target from another brand's manual may not fit your cell. Check yours.
Sources
Water weight: the University of Arizona Cooperative Extension rainwater storage handout lists water at 8.34 pounds per gallon. Density: USGS Water Science School, water density (1 g/mL, rounded). Parts per million definition: USGS Water Science Glossary. Gallon, pound, and imperial gallon: NIST Handbook 44 (2026), Appendix C, and NIST SP 811, Appendix B.8. Target salt, salt type, and the drain-to-lower method: Hayward SwimPure Plus owner's manual (part 092744 Rev C). Target salt example and sensor accuracy: Pentair IntelliChlor Installation and User's Guide.
Related calculators
- Pool Volume Calculator - find how many gallons your pool holds
- Percentage Calculator - quick percent math
- Sales Tax Calculator - add sales tax to a receipt
Frequently asked questions
How much salt do I need to add to my pool?
Multiply your pool gallons by 8.34, multiply that by the ppm you need to add, then divide by 1,000,000. The answer is in pounds. A 20,000 gallon pool that needs to go from 2,000 ppm to 3,200 ppm takes about 200 pounds of salt.
What salt level should I aim for?
Use the number in the manual for your salt chlorine generator. It depends on the model. For example, one Hayward manual lists 2,700 to 3,400 ppm with 3,200 ppm as optimal, and one Pentair IntelliChlor guide lists 3,600 to 4,500 ppm with 3,600 ppm as ideal. Check the label or manual of your salt cell.
How many pounds of salt raise a pool by 100 ppm?
For every 10,000 gallons, about 8.3 pounds of salt raise the level by 100 ppm. A 15,000 gallon pool takes about 12.5 pounds, and a 30,000 gallon pool takes about 25 pounds.
Why does the calculator show "No salt needed"?
Your current reading is already at or above your target. Adding more would push the level higher. If the level is too high, the only way to bring it down is to drain part of the pool and refill it with fresh water.
How much water do I drain to lower the salt level?
Drain the share given by 1 minus the target divided by the current level. If you are at 3,500 ppm and want 3,000 ppm, that is about 14.3% of the water. This assumes the fresh water has almost no salt, so retest after the pool has circulated.
Does it matter if my pool is measured in imperial gallons?
Yes. An imperial gallon is about 20% larger than a US gallon. This calculator uses US gallons, so convert first or switch to liters. If you enter liters, the calculator converts them to US gallons for you.
Should I add all the salt at once?
One Hayward manual says to add salt with the pump running and brush it around so it does not pile up on the floor. If you are not sure about your test reading, add a little less than the full amount, run the pump, and retest. One Pentair guide says its salt sensor reading is within plus or minus 500 ppm.