How to calculate how much salt to add
Salt level is measured in parts per million (ppm) by weight. One ppm means one pound of salt for every million pounds of water, and a gallon of water weighs about 8.34 lb. So the salt to add is the gap between the target and the current level, applied to the weight of the water in the pool.
Pounds of salt = gallons × (target ppm − current ppm) × 8.34 ÷ 1,000,000
Bags = pounds of salt ÷ 40, rounded up
A handy rule falls out of the formula: about 8.3 lb of salt per 1,000 gallons raises the level by 1,000 ppm. If you do not know your pool's volume, work it out first with the pool volume calculator.
Test the water before you add anything, with a salt test strip or a digital salt meter. The target comes from your salt system's manual, because the working range depends on the cell. The calculator starts with 3,200 ppm, a common target, and you can change it.
Worked example: a 15,000 gallon pool
A new 15,000 gallon pool filled with fresh water starts at about 0 ppm, and the salt system calls for 3,200 ppm.
- Salt needed: 15,000 × (3,200 − 0) × 8.34 ÷ 1,000,000 = 400.3 lb
- Bags of 40 lb: 400.3 ÷ 40 = 10.01, rounded up to 11 bags
Now suppose the same pool has dropped to 2,400 ppm after a lot of rain and refilling. It needs 15,000 × 800 × 8.34 ÷ 1,000,000 = 100.1 lb, which is 3 bags of 40 lb. Add the salt in stages and retest, rather than pouring in the full amount at once.
Salt needed by pool size
This table shows the salt for a fresh fill, from 0 ppm to 3,200 ppm. For a pool that already has some salt, use the calculator above, since only the gap needs to be filled.
| Pool volume | Pounds of salt | 40 lb bags |
|---|---|---|
| 5,000 gallons | 133.4 | 4 |
| 10,000 gallons | 266.9 | 7 |
| 15,000 gallons | 400.3 | 11 |
| 20,000 gallons | 533.8 | 14 |
| 25,000 gallons | 667.2 | 17 |
| 30,000 gallons | 800.6 | 21 |
Adding salt to a pool
Use salt sold for pools, and check your salt system's manual for any purity requirement. Turn the pump on, pour the salt into the water, and brush it around the floor to help it dissolve. Wait until it has dissolved and circulated, then retest before adding more. Always follow the product label and your salt system's instructions.
Salt does not evaporate. It is lost when water leaves the pool through splash-out, backwashing or draining, and it is diluted when rain or fresh water comes in. If the level ends up above the recommended range, the only fix is to drain some water and refill with fresh water. For the sanitizer side, the pool chlorine calculator shows how much chlorine to add when you need a boost.
Frequently asked questions
How many pounds of salt do I need per 1,000 gallons?
About 8.34 lb of salt raises the level of 1,000 gallons by 1,000 ppm. To go from 0 to 3,200 ppm that is about 26.7 lb per 1,000 gallons.
How many bags of salt do I need for a 15,000 gallon pool?
Starting from fresh water and aiming for 3,200 ppm, a 15,000 gallon pool needs about 400.3 lb of salt, which is 11 bags of 40 lb. If the pool already has some salt, you need fewer.
What salt level should a saltwater pool have?
It depends on the salt system. Many are set up around 3,200 ppm, but the recommended range is printed in your system manual, so use that figure as the target.
How do I lower the salt level in my pool?
Salt cannot be removed with a chemical. Drain part of the pool and refill it with fresh water, then retest. The calculator tells you when no salt is needed because the level is already at or above the target.
How do I add salt to a pool?
With the pump running, pour the salt into the water around the pool and brush it so it dissolves. Wait for it to circulate fully, retest, and add more only if the reading is still below the target.
More free calculators
These calculators give estimates for planning only. Densities, bag sizes and coverage vary by supplier, so confirm quantities before you order.