Pool salt calculator

The formula for any pool is pounds = ppm to add × gallons × 8.345 ÷ 1,000,000, so one 40 lb bag raises a 10,000-gallon pool by about 479 ppm.

Calculator: gallons, current and target salt, bag size

Enter your pool volume, the salt reading you have now (0 for a new fill), the target from your chlorinator's manual, and the bag size you buy. The result is the exact weight to add plus a shopping list rounded up to whole bags. Add the exact weight, not the whole last bag, unless you are well below your target.

Where does the salt reading come from? Your salt cell's display, a salt test strip, or a digital meter. They often disagree by a few hundred ppm. If the cell says "low salt" but a strip says 3,200, check the cell's reading against a second method before adding more. Cells that read incorrectly are a common reason pools end up with too much salt.

Your pool volume matters more here than for any other chemical, because you add salt by the hundreds of pounds. If you only know the size roughly, the pool volume calculator gets you close. After you add salt, you can work backward: the rise in your salt reading tells you how many gallons you really have.

Target salt by chlorinator brand (manual values)

Use the number printed in your own manual. Cells are built for a range. With too little salt, they stop producing chlorine. With too much, some shut down or wear out faster. Examples from manufacturer documents:

The calculator defaults to 3,200 ppm because both examples accept it. The pool salt level guide explains what happens at the low and high ends.

Chart: 500–40,000 gallons

Pounds of salt for a new fill to 3,200 ppm, the number of 40 lb bags, and a +500 ppm top-up, by pool size.

Pool salt by pool size

Pool size	0 → 3,200 ppm	40 lb bags	+500 ppm
500 gal	13.4 lb	1	2.1 lb
1,000 gal	26.7 lb	1	4.15 lb
2,000 gal	53.4 lb	2	8.35 lb
3,000 gal	80.1 lb	3	12.5 lb
4,000 gal	107 lb	3	16.7 lb
5,000 gal	134 lb	4	20.9 lb
6,000 gal	160 lb	5	25.0 lb
7,000 gal	187 lb	5	29.2 lb
8,000 gal	214 lb	6	33.4 lb
10,000 gal	267 lb	7	41.7 lb
12,000 gal	320 lb	9	50.1 lb
15,000 gal	401 lb	11	62.6 lb
20,000 gal	534 lb	14	83.5 lb
25,000 gal	668 lb	17	104 lb
30,000 gal	801 lb	21	125 lb
40,000 gal	1,068 lb	27	167 lb

Each size links to its full dose chart.

Download this data (CSV)

Topping up is more common than a new fill. For a 15,000-gallon pool (one 40 lb bag adds about 320 ppm):

Handy numbers for one 40 lb bag: about +479 ppm in 10,000 gallons, +320 ppm in 15,000, +240 ppm in 20,000, +192 ppm in 25,000, and +160 ppm in 30,000 gallons.

What salt to buy (99%+, no iodine or anti-caking agents)

Buy salt sold for pools or water softeners that is at least 99% sodium chloride. Avoid anything with iodine, anti-caking agents, or other additives: you are adding hundreds of pounds, and whatever else is in the bag ends up in your water. Hayward's guidance is the same: high-purity salt without additives. Rock salt and table salt are the usual mistakes. Fine-grain pool salt dissolves fastest; pellets work but take longer to dissolve.

Wait 24 hours before you retest

1. Many manuals say to turn the chlorinator off (or set output to 0%) while you add salt; check yours. Keep the pump running.
2. Pour the salt around the shallow end or the perimeter, not into the skimmer.
3. Brush until it dissolves, so no piles sit on the floor.
4. Run the pump for about 24 hours so the salt spreads evenly. Hayward notes the reading settles in about a day.
5. Test salt again, then turn the chlorinator back on at your usual output.

Testing too early is how pools get too much salt: the cell still reads "low," and someone adds another bag. For daily care of a salt pool (pH drift, cell cleaning, stabilizer), see salt water pool care. Scale on the plates also makes readings unreliable. Clean the salt cell if it looks crusty.

Too much salt?

Salt does not evaporate, and no chemical removes it. The only fix is replacing water. With salt-free fill water, replace 20% of the water to go from 4,000 to 3,200 ppm, or 36% to go from 5,000 to 3,200 ppm. Moderately high salt is usually a nuisance rather than an emergency. But some cells show errors or stop above their range, and high salt adds to corrosion of metal parts. Drain in stages, refill, circulate for 24 hours, and retest. The drain math is the same as for stabilizer: see the drain calculator on the CYA page. If you are still deciding whether salt is for you, compare salt water vs chlorine pools.

FAQ

How many 40lb bags of salt do I need for my pool?

For a new fill to 3,200 ppm: about 7 bags for 10,000 gallons, 11 for 15,000, 14 for 20,000, and 21 for 30,000. For a top-up, one 40 lb bag adds about 479 ppm per 10,000 gallons, so divide the ppm you need by that number and scale for your size.

How do I calculate the amount of salt needed for my pool?

Pounds of salt = (target ppm − current ppm) × gallons × 8.345 ÷ 1,000,000. The 8.345 is the weight of one gallon of water in pounds. Example: 15,000 gallons from 0 to 3,200 ppm is 3,200 × 15,000 × 8.345 ÷ 1,000,000 ≈ 401 lb.

How often should I add a bag of salt to my pool?

Only when water leaves the pool: backwashing, splash-out, rain overflow, or draining. Evaporation leaves the salt behind. Many pools need a bag or two after heavy rain or at season opening, and little in between. Test monthly and add only what the calculator shows.

Sources

• Hayward, AquaRite manual: PDF; How much salt do you add: hayward.com
• Pentair, IntelliChlor SCG Quick Start Guide and Tips (P/N 520943 Rev. D): PDF
• Our formulas and the Hayward cross-check (267 lb for 0 → 3,200 ppm in 10,000 gallons): methodology