Enter your volume, your current salt level and your target. The calculator gives you pounds, bags, and if you are above target, how much water you need to replace instead.

How it works

Salt dosing is straightforward arithmetic. One pound of salt in 1,000 gallons of water raises salinity by about 120 ppm, because 1,000 gallons of water weighs roughly 8,345 pounds.

pounds of salt = (gallons × ppm increase) ÷ 120,000

A 40 lb bag therefore moves 10,000 gallons by about 480 ppm. Sanity-check any chart you find against that.

Going the other direction, there is no chemical that removes salt. You replace water:

fraction to replace = 1 − (target ppm ÷ current ppm)

Pool salt chart

Pounds of salt by pool volume, from the same formula the calculator uses: pounds = (gallons × ppm increase) ÷ 120,000. Bags are 40 lb, rounded up to the nearest half bag so you are not left short.

Pool volume	Startup, 0 to 3,200 ppm	40 lb bags	Per 100 ppm raise	Per 500 ppm raise
5,000 gal	133 lb	3.5	4.2 lb	20.8 lb
10,000 gal	267 lb	7	8.3 lb	41.7 lb
12,000 gal	320 lb	8	10.0 lb	50.0 lb
15,000 gal	400 lb	10	12.5 lb	62.5 lb
18,000 gal	480 lb	12	15.0 lb	75.0 lb
20,000 gal	533 lb	13.5	16.7 lb	83.3 lb
25,000 gal	667 lb	17	20.8 lb	104.2 lb
30,000 gal	800 lb	20	25.0 lb	125.0 lb

Two rows people search for, worked out:

15,000 gallons from zero: (15,000 × 3,200) ÷ 120,000 = 400 lb, which is 10 bags of 40 lb.
20,000 gallons from zero: (20,000 × 3,200) ÷ 120,000 = 533 lb, which is 13.3 bags, so 13 and a half bags covers it.

A startup figure assumes water with no salt in it. Tap water and any previous salt add to that, so test before you buy the full amount, and add half first.

Pick your target from your equipment, not from a round number

Most calculators default to 3,200 ppm. That is a reasonable middle, but your manufacturer’s window is the number that matters, and running below it makes your cell work harder for the same chlorine. Typical residential ranges fall between 2,700 and 3,400 ppm depending on the system. Check your manual, and aim for the middle of your window rather than the bottom, so a heavy rain does not drop you into a low-salt warning.

Before you trust the answer

Two inputs can wreck a perfectly correct calculation.

Your volume. If you are using a figure from a builder, a listing or the side of a box, it could be out by 20% or more, and your dose will be out by the same margin. The average depth trap is where most of that error comes from. Measure once properly and you will use the number for years.

Your current reading. If it came off your control panel, be careful. Salt systems infer salinity from conductivity rather than measuring salt, so scale, plate wear, cold water or the wrong cell model set in the menu all move the display with no salt moving. Get a water test before you dose. Which reading to trust walks through it.

Then do these two things

Add half, wait a day, retest. Salt needs time to dissolve and distribute. A reading two hours after pouring tells you nothing.

Brush it off the floor. Salt dumped in one spot stays there. This is the single reason behind nearly every “I added six bags and nothing happened” story, including the owner who put twelve bags into a pool they thought held 8,403 gallons and still read 500 ppm, whose actual problem was the volume figure.

If your pool is under about 8,000 gallons, weigh out partial bags. A full 40 lb bag in a 5,600 gallon pool is an 860 ppm jump, which is a lot to take back.

If you are already over target

Use the drain-down planner instead. It works out gallons to replace, inches off the surface, and what the partial drain does to your calcium hardness, cyanuric acid and alkalinity, which is the part that catches people out.

Worried your reading is the problem rather than your salt? The Salt Cell Protection Kit has the reconciliation decision tree, brand-specific target ranges, the cell health test and the cell-type audit that catches a panel configured for the wrong cell. $47.