Pool Salt Calculator

Enter your pool volume and the salt reading from your test, and this calculator gives the pounds of pool salt to add, the number of 40 lb and 50 lb bags, and, if the pool is above target, the share of water to drain. A 20,000 gallon pool filled with fresh water needs about 534 lb to reach 3,200 ppm.

By Ellyana, creator of CalcClearly · Last updated 2026-10-19

Pool Details

Pool volume

Units

Do you know your current salt level?

Target salt level (ppm)

Your salt dosage will appear here

Enter your pool volume and salt level, then click calculate.

Salt needed by pool size

Pounds of pool salt at 3,200 ppm, from a fresh fill and as a top-up from 2,800 ppm. Bags are rounded up.

Pool size	0 → 3,200 ppm	40 lb bags	2,800 → 3,200 ppm	40 lb bags
10,000 gal	266.9 lb	7	33.4 lb	1
15,000 gal	400.3 lb	11	50.0 lb	2
20,000 gal	533.8 lb	14	66.7 lb	2
25,000 gal	667.2 lb	17	83.4 lb	3
30,000 gal	800.6 lb	21	100.1 lb	3

Quick Answer

Pounds of salt = ppm to add × gallons × 8.34 ÷ 1,000,000. About 8.3 lb per 10,000 gallons raises the level by 100 ppm. A 20,000 gallon pool at 0 ppm needs 534 lb to reach 3,200 ppm (14 bags of 40 lb), and one at 2,800 ppm needs 66.7 lb. Hayward's AquaRite manual gives 2,700 to 3,400 ppm as its range, but check your own salt cell's manual.

How It Works: Formula & Variables

lbs of salt = (Target ppm − Current ppm) × Gallons × 8.34 ÷ 1,000,000

8.34: The weight of one gallon of water in pounds. One ppm of salt in a gallon is therefore 8.34 ÷ 1,000,000 lb.
Liters: Divide by 3.785 to get gallons first.
Current level unknown: Taken as 0 ppm, which is right for a fresh fill and too high for a pool that already has salt in it.
Too much salt: Share of water to replace = 1 − Target ÷ Current. Fresh water has no salt, so the mix is diluted in proportion.

Worked Examples

Example 1: a new pool, filled with fresh water

A 20,000 gallon pool starts at 0 ppm and needs to reach 3,200 ppm. Pounds = 3,200 × 20,000 × 8.34 ÷ 1,000,000 = 534 lb, which is 14 bags of 40 lb or 11 bags of 50 lb.

Example 2: topping up after a wet spring

The same pool tests at 2,800 ppm after heavy rain and an overflow. It needs 400 ppm more, so pounds = 400 × 20,000 × 8.34 ÷ 1,000,000 = 66.7 lb, which is 2 bags of 40 lb with some left over. Add part of it, wait about a day, and retest.

Example 3: too much salt

A pool reads 4,000 ppm and the target is 3,200. Share to replace = 1 − 3,200 ÷ 4,000 = 20%. In a 20,000 gallon pool that is about 4,000 gallons drained and refilled with fresh water, then retested.

Key Concepts

Salt is not used up. The generator splits dissolved salt into chlorine and the chlorine turns back into salt as it works. The level falls only when water leaves the pool.

The target comes from your salt cell. Hayward's AquaRite manual gives 2,700 to 3,400 ppm as ideal with 3,200 ppm as optimum. It says low salt reduces chlorine output and that high salt can shut the unit down. Other makers use different figures, so read yours.

Your test reading matters as much as the maths. Test strips and drops are rough at this range. If a result looks odd, retest with a second method before adding or draining hundreds of pounds' worth.

Common Mistakes

Using the wrong salt: Rock salt, iodized table salt and products with anti-caking agents can discolor surfaces and foul the cell. Buy pool-grade sodium chloride.

Retesting too soon: Undissolved salt gives a low reading, so you add more, then overshoot. Run the pump and wait about 24 hours first.

Adding the full amount from a guessed starting point: If you do not know the current level, test first. Adding for 0 ppm to a pool that already has salt in it overshoots, and the only way back is draining.

Aiming for a different number than the cell wants: The generic target here is a starting point. Use the range in your own manual.

Frequently Asked Questions

To fill a 20,000 gallon pool with fresh water up to 3,200 ppm takes about 534 lb of pool salt, which is 14 bags of 40 lb or 11 bags of 50 lb. If the pool already reads 2,800 ppm, topping up to 3,200 takes only 66.7 lb. The sum is pounds = ppm to add × gallons × 8.34 ÷ 1,000,000.

It depends on the salt cell. Hayward's AquaRite manual gives 2,700 to 3,400 ppm as the ideal range and 3,200 ppm as optimum, and says low salt cuts chlorine output while high salt can shut the unit down. Other makers publish their own figures, so look up the target in your cell's manual. This calculator starts at 3,200 ppm and you can type over it.

Divide the pounds by the bag size and round up. Pool salt is sold in 40 lb and 50 lb bags in the US, so a 400 lb job (a 15,000 gallon pool from zero to 3,200 ppm) is 11 bags of 40 lb or 9 bags of 50 lb. Buying one bag too many is cheaper than stopping halfway, since you can retest after the first batch has dissolved and add the rest.

Use pool-grade sodium chloride, not rock salt or iodized table salt. A Hayward-branded salt chlorinator summary says at least 99% pure, and pool retailer InyoPools recommends evaporated, granulated, non-iodized salt at 99.8% or better, without anti-caking agents such as sodium ferrocyanide because they can discolor fittings and pool surfaces. Never use calcium chloride.

Pool equipment guides tell you to spread the salt around the pool with the pump running, then wait about 24 hours before retesting. Retesting too early gives a low reading because the salt has not yet mixed through the water, and that leads people to add more than they need.

Salt does not evaporate, so the level only falls when water leaves the pool: splash-out, backwashing, and rain overflow or a partial drain. Test it when you open the pool, after heavy rain, and whenever your salt cell shows a low-salt warning, then add only the difference between the reading and your target.

There is no chemical that removes salt. You drain part of the pool and refill with fresh water. The share you need to replace is 1 − target ÷ current. A pool at 4,000 ppm that should be at 3,200 needs about 20% of its water replaced. Enter your current and target readings in the calculator and it works out the drain percentage and gallons for you.

Yes. You install a salt chlorine generator, then add salt up to the target in the cell manual. Whether you need to drain first depends on your water chemistry, not on the conversion. If cyanuric acid has built up from years of stabilized chlorine, check the generator manual for the maximum it allows.

Last reviewed 2026-10-19. For educational purposes only — not professional advice.

Sources

The 8.34 lb per gallon figure is the weight of water, so the formula is arithmetic rather than a published rule.