# How much pool salt to add?

Works out how many pounds or kilograms of salt to add to a saltwater pool to reach a target salt level in ppm, the bags to buy, or how much water to drain when the level is too high.

- Page: https://www.acalculator.org/construction/pool-salt-calculator
- JSON spec: https://www.acalculator.org/construction/pool-salt-calculator.json
- Version: 2bd177a58858

## Default answer

Example with the default inputs (Pool volume 15,000 gal, Current salt level (ppm) 500, Target salt level (ppm) 3,200, Bag size 40 lb): Add 338 lb of salt to reach 3,200 ppm.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| v | Pool volume | How much water the pool holds. |
| cur | Current salt level (ppm) | The salt level a test strip or meter reads now, in parts per million. |
| tgt | Target salt level (ppm) | The salt level your chlorine generator asks for, often 3,200 ppm. |
| bag | Bag size | How much salt one bag holds, often 40 lb. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| salt | Salt to add | (target − current) ppm × litres of water ÷ 1,000,000 kg; 0 when the level is already at or above the target. |
| bags | Bags to buy | The salt to add ÷ the bag size, rounded up to whole bags. |
| perBag | One bag raises the level by (ppm) | The bag’s salt in milligrams ÷ litres of water. |
| drainShare | Water to drain and refill | 1 − target ÷ current, when the current level is above the target: the share of the water to replace with fresh water. |
| drain | Volume to drain | The pool volume × the share to drain. |
| litres | Water in liters | The pool volume in liters. |

## Method

salt (kg) = (target − current) ppm × liters ÷ 1,000,000, with 1 ppm = 1 mg/L; bags = ⌈salt ÷ bag⌉; drain share = 1 − target ÷ current.

## Assumptions

- One ppm of salt is one milligram per liter of water, the usual reading of pool test strips and meters.
- Salt dissolves fully and mixes through the whole pool. Water you add or lose later changes the level.
- Draining assumes you refill with fresh water that has no salt.
- Typed numbers are read exactly, so a volume in gallons and a level in ppm give exact amounts, rounded once for display.

## Worked examples

1. v = 37.854118, cur = 0, tgt = 3,200, bag = 18.143695 gives salt = 121.133177, bags = 7, perBag = 479.305709, litres = 37,854.11784. Source: U.S. Geological Survey, National Field Manual / IFM conversion factors (1 milligram per liter is about 1 part per million in water), https://pubs.usgs.gov/of/2000/ofr00-213/manual_eng/conversion.html (retrieved 2026-10-02); NIST Special Publication 811, Appendix B (1 US gallon = 3.785411784 L; 1 lb = 0.45359237 kg exactly), https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02).
2. v = 56.781177, cur = 2,400, tgt = 3,200, bag = 18.143695 gives salt = 45.424941, bags = 3. Source: U.S. Geological Survey, National Field Manual / IFM conversion factors (1 milligram per liter is about 1 part per million in water), https://pubs.usgs.gov/of/2000/ofr00-213/manual_eng/conversion.html (retrieved 2026-10-02); Hayward Pool Products, How to Lower Salt Levels Within a Swimming Pool (2,700 to 3,400 ppm, best at 3,200 ppm; drain and refill a share of the water), https://www.hayward.com/blog/post/how-to-lower-salt-levels-within-swimming-pool (retrieved 2026-10-02).
3. v = 37.854118, cur = 4,000, tgt = 3,500 gives salt = 0, drainShare = 12.5%, drain = 4.731765. Source: Hayward Pool Products, How to Lower Salt Levels Within a Swimming Pool (2,700 to 3,400 ppm, best at 3,200 ppm; drain and refill a share of the water), https://www.hayward.com/blog/post/how-to-lower-salt-levels-within-swimming-pool (retrieved 2026-10-02): a 10,000 gallon pool at 4,000 ppm, drain about 1/8.
4. v = 50, cur = 0, tgt = 3,000 gives salt = 150, litres = 50,000. Source: U.S. Geological Survey, National Field Manual / IFM conversion factors (1 milligram per liter is about 1 part per million in water), https://pubs.usgs.gov/of/2000/ofr00-213/manual_eng/conversion.html (retrieved 2026-10-02).

## FAQ

### How much salt do I need for my pool?

Multiply the rise in ppm by the liters of water and divide by 1,000,000 to get kilograms (1 ppm = 1 mg per liter). A new 10,000 gallon pool (37,854 L) at 3,200 ppm needs 3,200 × 37,854 ÷ 1,000,000 = 121.1 kg, about 267 lb or 7 bags of 40 lb.

### What salt level should a saltwater pool have?

Use the number in your chlorine generator’s manual. Hayward, for example, gives 2,700 to 3,400 ppm with 3,200 ppm as the best level. Too little salt cuts chlorine output; too much can shut the generator down and makes the water taste salty.

### How much does one 40 lb bag raise the salt level?

A 40 lb bag is 18.14 kg, or 18,143,695 mg. In 10,000 gallons (37,854 L) that is 18,143,695 ÷ 37,854 ≈ 479 ppm. In a bigger pool the same bag raises the level less.

### How do I lower the salt level?

Salt does not evaporate or wear out, so the only way down is to drain some water and refill with fresh water. Drain the share 1 − target ÷ current: from 4,000 ppm to 3,500 ppm, drain 1 − 3,500 ÷ 4,000 = 12.5%, which is 1,250 gallons of a 10,000 gallon pool.

### Why add the salt in steps?

Salt takes time to dissolve and mix, and test strips have some error. Add most of the amount, run the pump for a day, test again, and then add the rest. That way you do not overshoot and have to drain water.

## Sources

- U.S. Geological Survey, IFM conversion factors (milligrams per liter and parts per million in water). https://pubs.usgs.gov/of/2000/ofr00-213/manual_eng/conversion.html (retrieved 2026-10-02)
- Hayward Pool Products, How to Lower Salt Levels Within a Swimming Pool (2,700 to 3,400 ppm, best 3,200 ppm; drain and refill to lower the level; a 10,000 gallon pool at 4,000 ppm drains about 1/8). https://www.hayward.com/blog/post/how-to-lower-salt-levels-within-swimming-pool (retrieved 2026-10-02)
- NIST Special Publication 811, Appendix B (1 US gallon = 3.785411784 L, 1 ft³ = 28.316846592 L, 1 lb = 0.45359237 kg, exactly). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)