Pool salt calculator

Enter your pool's volume, your current salt reading and the level your salt chlorine generator wants. You'll get the pounds of salt to add and the number of bags. If your salt is too high, it tells you how much water to replace instead.

Pool volume

Volume unit

Current salt (ppm)

Target salt (ppm, from your cell's manual)

Bag size (lb)

Salt to add

–

Bags

–

Don't know your volume? Use the pool volume calculator.

Use your generator's number. Salt chlorine generators are designed for a specific salt range, and it differs between makers and models. One major brand lists 2,700–3,400 ppm with 3,200 ppm as ideal, others call for 3,000–3,500 ppm or 3,600 ppm, and some units run at 4,000 ppm or more. Too little salt and the cell makes less chlorine or shuts off. Too much can damage some cells. The default of 3,200 ppm here is common, but your manual is the authority.

The formula

Salt (lb) = (target ppm − current ppm) × pool gallons × 8.345 ÷ 1,000,000
Salt (kg) = (target ppm − current ppm) × pool liters ÷ 1,000,000

A part per million (ppm) of salt is one pound of salt per million pounds of water. A US gallon of water weighs about 8.345 lb, so a gallon count times 8.345 gives the water's weight in pounds. In metric it's simpler, because a liter of water weighs a kilogram: 1 ppm is 1 mg per liter.

Worked examples

Topping up: 15,000 gallons from 2,600 to 3,200 ppm

(3,200 − 2,600) × 15,000 × 8.345 ÷ 1,000,000 ≈ 75 lb, a little under two 40-lb bags.

A new saltwater pool: 15,000 gallons from 0 to 3,200 ppm

3,200 × 15,000 × 8.345 ÷ 1,000,000 ≈ 400 lb, or about ten 40-lb bags. Fill water usually has a little salt already, so test before you start and enter that reading as the current level.

A quick rule of thumb

Raising 10,000 gallons by 100 ppm takes about 8.3 lb of salt. Scale it up or down for your pool.

How to add salt

Turn the salt cell off (or set its output to zero) while you add salt, and leave the pump running.
Use pool salt: plain sodium chloride, at least 99% pure, without anti-caking agents or iodine. Many generator makers advise against rock salt, which can carry impurities that stain.
Pour it around the shallow end or into the deep end, not into the skimmer, unless your manual says otherwise. Brush any piles on the floor until they dissolve.
Circulate for 24 hours, then retest before adding more. Add a bit less than the calculated amount if you're unsure: adding more is easy, but taking salt out means draining water.
Turn the cell back on.

Testing salt

Most generators display a salt reading, but the cell's estimate can drift, especially as the cell ages or the water is cold. Check it now and then with salt test strips or a drop test kit. If the cell's display and your test disagree, follow the manufacturer's troubleshooting steps before adding salt based on the display alone.

Lowering salt that's too high

Salt doesn't evaporate and isn't used up by the generator. Water lost to evaporation leaves the salt behind, so levels stay put until water is splashed out, backwashed or drained. The only practical way to lower salt is to replace some water. Replacing 20% of the water lowers salt by about 20%. The drain and refill calculator works it out for any target.

Frequently asked questions

How much salt does a saltwater pool lose each year?

Only what leaves with the water: splash-out, backwashing, rain overflow and draining. Pools that backwash often or get heavy rain need more top-ups. Evaporation doesn't remove salt.

Can I swim right after adding salt?

Salt at these levels is gentle. It's around a tenth of the saltiness of seawater. Most people wait until it has dissolved and mixed. Check the instructions on your chlorinator and salt bags.

Does salt raise pH?

Salt itself doesn't. But saltwater pools often see pH drift upward, because the cell's chlorine production and the bubbling in the cell push pH up. See our saltwater pool guide.