Pool Salt Calculator

How to work it out

1. Test the salt level

   Use test strips or take a sample to the pool store. Do not trust the chlorinator's own display for this — it drifts, and a reading that is wrong by 400 ppm is a common reason a cell stops making chlorine.

2. Work out the gap

   Salt only leaves the pool with water — splash-out, backwashing, rain overflow. It is not used up making chlorine, so a pool that was right last month is usually only a little low now.

3. Add it with the pump running

   Broadcast the salt across the shallow end with the pump on. Brush it around until it dissolves rather than leaving a pile on the floor, which can stain plaster.

4. Wait before you retest

   Give it 24 hours of circulation before testing again. Turn the chlorinator off until the salt has dissolved and the reading is back in range.

Salt needed for a new pool

Pounds of pool salt to take a freshly filled pool from 0 to 3,200 ppm, and the 40 lb bags that means.

Pool volume	Salt needed	40 lb bags
10,000 gal	267 lb	7
15,000 gal	400 lb	10
20,000 gal	534 lb	14
25,000 gal	667 lb	17
30,000 gal	801 lb	20

What one 40 lb bag does

How far a single bag moves the reading, by pool size.

Pool volume	One bag raises salt by
10,000 gal	480 ppm
15,000 gal	320 ppm
20,000 gal	240 ppm
25,000 gal	192 ppm
30,000 gal	160 ppm

How much salt does a saltwater pool need?

Most chlorine generators want between 2,700 and 4,500 ppm, and run best around 3,200 ppm. Below the range the cell stops producing; well above it, the cell and any metal fittings wear faster.

Filling from zero takes roughly 27 lb of salt per 1,000 gallons to reach 3,200 ppm — ten 40 lb bags for a 15,000 gallon pool.

Use pool salt, not table salt

Buy salt sold for pools: it is at least 99.8% pure sodium chloride, with no iodine and no anti-caking agents. Water softener salt in crystal form works if it is pure, but it dissolves slowly.

Avoid rock salt and anything with yellow prussiate of soda added, which stains. Never use iodized table salt.

If the level is too high

There is no chemical that removes salt. The only fix is to drain part of the pool and refill with fresh water, which the calculator estimates for you.

High salt usually means someone dosed from a wrong volume figure, or added a second batch before the first had dissolved and been retested.

Why the level drifts down

Backwashing, splash-out, draining after heavy rain and leaks all take salt with the water. Evaporation does not — the salt stays behind, so a pool that only loses water to evaporation gets slightly saltier.

Test monthly through the season, and always after a big top-up.

How this is worked out

No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.

1. gap = target ppm − current ppm How far the reading has to move.
2. pounds = gallons × gap × 8.34 ÷ 1,000,000 A gallon of water weighs 8.34 lb, and ppm is parts per million by weight.
3. bags = pounds ÷ bag size, rounded up Salt is sold in 40 lb bags in most of the US.
4. water to replace = gallons × (current − target) ÷ current Only when the pool is over target, since nothing removes salt but dilution.

Common questions

How much salt do I need for a 15,000 gallon pool?

About 400 lb, or ten 40 lb bags, to go from a fresh fill to 3,200 ppm.

How many ppm does one bag of salt add?

A 40 lb bag adds about 320 ppm to 15,000 gallons, or 480 ppm to 10,000 gallons. The figure for your pool is shown above.

What salt level should a pool be?

Follow the chlorinator manual. Most want 2,700–4,500 ppm with 3,200 as a good working target.

Can I use water softener salt in my pool?

Only if it is pure sodium chloride with no additives. Pool salt is ground to dissolve quickly; softener pellets take far longer and are easy to leave sitting on the floor.

How do I lower the salt level?

Drain part of the pool and refill with fresh water — nothing else removes salt. Replacing a tenth of the water lowers the reading by roughly a tenth.

Does salt get used up making chlorine?

No. The cell splits salt into chlorine, which then reverts to salt after it has done its work. You only lose salt with water that leaves the pool.

How long before I can swim?

Once the salt has fully dissolved, usually within a few hours of brushing with the pump running. Leave 24 hours before testing so the reading is accurate.

Is a saltwater pool chlorine-free?

No. A salt pool makes its own chlorine from the salt instead of you adding it. The water is gentler because the chlorine is produced steadily and at low concentration, not because there is none.

Where these figures come from

Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.

• Salt chlorine generator manufacturer manuals — operating ranges of 2,700–4,500 ppm and typical 3,200 ppm targets
• Association of Pool & Spa Professionals water chemistry guidance — salt purity requirements and dosing practice
• NIST Special Publication 811 — the 8.34 lb per gallon weight of water used for ppm dosing

Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 27, 2026.