Salt level controls how much chlorine your generator produces. Before calculating salt, you need your pool's volume in gallons. The Pool Volume Calculator converts pool dimensions to gallons for any shape.
The formula converts parts per million to physical weight using water's density. One US gallon weighs 8.34 pounds, so 1 ppm in 1,000 gallons equals 0.00834 pounds of dissolved substance.
Worked example: An 18,000-gallon pool at 900 ppm targeting 3,200 ppm needs: 18,000 x 2,300 / 1,000,000 x 8.34 = 345.3 lbs. That is 9 bags of 40 lb salt (360 lbs total). Bag counts always round up so you reach the target rather than fall short.
Bag counts round up because partially filling a bag does not lower your total add amount. For other construction projects requiring precise material counts, the Concrete Bag Calculator follows the same ceiling logic.
The table below shows pounds and 40 lb bags needed to bring common pool sizes from 0 ppm to 3,200 ppm. If your pool already has salt, subtract your current reading from 3,200 before using this as a reference.
| Pool Size | Gallons | Lbs Needed | 40 lb Bags |
|---|---|---|---|
| 15 ft round | 5,300 | 141.3 | 4 |
| 16x32 rectangular | 15,000 | 400.3 | 11 |
| 18 ft round | 7,600 | 202.7 | 6 |
| 18x36 rectangular | 18,000 | 480.4 | 13 |
| 24 ft round | 13,500 | 360.3 | 10 |
| 20x40 rectangular | 24,000 | 640.5 | 17 |
For measuring the surrounding deck or patio area, the Square Footage Calculator gives exact square footage from any dimensions. Bag counts here use coarse pool-grade salt; fine-grain salt delivers the same weight but may compact differently.