Pool Salt Calculator

How to use the pool salt calculator

1. Give it your pool volume. Type it in US gallons, Imperial gallons, litres or cubic metres. If you don’t know it, switch to Work it out from measurements and enter the length, width and depth instead — you don’t have to leave this page to find it.
2. Pick your salt system. Hayward, Jandy and Pentair fill in their own target level. Pick Something else to type the number from your manual.
3. Enter your current reading from a test strip, a meter or the chlorinator display. Use 0 if the pool is fresh water.
4. Set your bag size. 40 lb, 50 lb, 25 kg, whatever you’re actually buying. You get the weight of salt and the number of whole bags.

How much salt to add to a pool

The whole calculation is one line, and it needs no fudge factor:

kilograms of salt = litres of water × ppm rise ÷ 1,000,000

That works because ppm in water means milligrams per litre, by definition. A million milligrams is a kilogram, so the units cancel and nothing is approximated.

US pool sites usually write it as pounds = gallons × ppm × 8.345 ÷ 1,000,000, where 8.345 is the weight of a US gallon of water in pounds. That constant is a rounded conversion, not physics — the exact figure is 8.3454045. We work in litres and convert at the end, so it never appears.

Checked against two manufacturers’ own charts

Hayward and Jandy both publish dosing tables in their installation manuals. This calculator reproduces both, at every volume they list.

Hayward truncates its column to whole pounds, 8,000 gallons is really 213.6 lb and they print 213. Jandy rounds instead: its table gives 376 lb for 15,000 gallons at 3,000 ppm, where the exact figure is 375.5. Two makers, two conventions, one formula underneath. We keep the unrounded number and let the bag count do the rounding, because rounding the dose down would only ever leave you short.

What salt level your pool should be

This is the part most calculators get wrong, and it isn’t a small difference.

Read from the Hayward Aqua Trol, Jandy Pro Series TruClear, and Pentair IntelliChlor IC15/20/40/60 manuals on 22 September 2026.

Look at where those ranges sit. Pentair’s minimum of 3,600 ppm is higher than both Hayward’s and Jandy’s maximums. There is no single number that keeps all three happy, which is exactly why this calculator asks instead of assuming.

It matters in bags. For a 10,000 gallon pool starting from fresh water, Hayward’s 3,200 ppm needs 267 lb and Pentair’s 3,600 ppm needs 300 lb — 33 lb more, very nearly a whole extra 40 lb bag. Dose a Pentair pool to the 3,200 ppm that most calculators default to and you finish 400 ppm below the minimum Pentair specifies, with the cell running in low salt.

How many bags of pool salt do I need?

Divide the weight by your bag size and round up. You can’t buy 0.68 of a bag.

A 10,000 gallon pool, fresh water to 3,200 ppm. Every calculator we checked on page 1 either assumes a 40 lb bag without asking or doesn’t count bags at all, and one of them reports “~1.5 bags”, which is not a thing you can put in a trolley.

The useful sanity check is what a single bag does. One 40 lb bag in a 10,000 gallon pool moves it about 479 ppm. If your reading is 200 ppm low, you need part of one bag, not a pallet.

How to lower a high salt level

Drain some water and refill with fresh. That’s the only option, nothing removes salt chemically. Hayward’s manual says it in one sentence: the only way to lower the concentration is to partially drain the pool and refill with fresh water.

Fresh water is 0 ppm, so replacing a fraction of the water leaves that fraction less salt:

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

From 4,000 down to 3,200 ppm: (4,000 − 3,200) ÷ 4,000 = 20% of the water. In a 10,000 gallon pool that’s 2,000 gallons.

Drain in stages and retest between each one. Never empty a pool to chase a number — a drained shell can float out of the ground when the water table is high, and a vinyl liner can shrink and split once it dries.

A worked example

A rectangular pool, 32 ft by 16 ft, sloping from 3 ft at the shallow end to 7 ft at the deep end. The strip reads 1,800 ppm. It’s a Hayward system, so the target is 3,200. Salt comes in 40 lb bags.

1. Average depth. (3 + 7) ÷ 2 = 5 ft.
2. Volume. 32 × 16 × 5 = 2,560 cubic feet, which is 19,150 US gallons — about 72,491 litres.
3. Rise needed. 3,200 − 1,800 = 1,400 ppm.
4. Salt. 72,491 × 1,400 ÷ 1,000,000 = 101.5 kg, or 223.7 lb.
5. Bags. 223.7 ÷ 40 = 5.6, so 6 bags, leaving about 16 lb spare.

Had the same pool been on a Pentair IntelliChlor, the target would be 3,600 ppm, the dose 287.7 lb, and the answer 8 bags — two more, from the same pool and the same reading.

What the calculator assumes

• Average depth. A sloping floor is treated as (shallow + deep) ÷ 2. That’s exact for a floor that slopes evenly and close enough for a typical hopper bottom.
• Oval pools are true ellipses. Area is π × half-length × half-width, which is 78.5% of the surrounding rectangle. Some pool sites use a 0.89 factor instead, which overstates an oval pool by about 13%.
• Depth is the depth of the water, not the height of the wall. Most pools sit four to six inches below the top.
• Refill water is 0 ppm. If yours is softened or naturally saline, the drain will get you less far than the number says.
• The salt dissolves fully. Add it with the chlorinator off, brush it across the floor until it’s gone, and run the pump for 24 hours before retesting.

Nothing you type leaves your browser

The calculation runs in JavaScript on your own device. Your pool’s dimensions and readings are never sent anywhere, never stored, and never put in the URL. Close the tab and they’re gone.