Pool Salt Calculator
A pool salt calculator uses lbs = (target − current ppm) ÷ 1,000,000 × gallons × 8.34. A 15,000 gal pool from 0 to 3,200 ppm needs 400 lb, or 11 bags.
Pool salt calculator: pounds and bags to reach your target ppm
A pool salt calculator solves a concentration problem. Salt level is measured in parts per million, and a gallon of water weighs about 8.34 lb. So raising a pool by 1 ppm takes 8.34 lb for every million gallons. The formula is lbs = (target ppm − current ppm) ÷ 1,000,000 × gallons × 8.34. A 15,000-gallon pool going from 0 to 3,200 ppm needs about 400 lb, which is 11 forty-pound bags.
The formula in plain words
Imagine the pool as a million small scoops of water. Every ppm means one scoop out of those million is salt. To get 3,200 scoops of salt in, you add salt by weight until its share reaches that number.
- Gap = target ppm − current ppm (never below zero)
- Pounds = gap ÷ 1,000,000 × gallons × 8.34
- Bags = pounds ÷ 40, rounded up
If you are already above target, the gap is zero and the calculator tells you to add none.
Worked examples
- New 15,000 gal pool, 0 ppm to 3,200 ppm
- Gap: 3,200 ppm
- Salt: 3,200 ÷ 1,000,000 × 15,000 × 8.34 = 400.3 lb
- Bags: 400.3 ÷ 40 = 10.01, rounded up to 11 bags
- 20,000 gal pool at 1,200 ppm, topping up to 3,200 ppm
- Gap: 3,200 − 1,200 = 2,000 ppm
- Salt: 2,000 ÷ 1,000,000 × 20,000 × 8.34 = 333.6 lb
- Bags: 333.6 ÷ 40 = 8.34, rounded up to 9 bags
Example 1 sits right on a bag boundary. The raw answer is 400.3 lb, just over ten bags, so the calculator rounds up to eleven. You would end up with about 40 lb extra, which you can store for the next top-up.
Salt from a fresh start to 3,200 ppm
| Pool size | Salt needed | 40-lb bags |
|---|---|---|
| 10,000 gal | 267 lb | 7 |
| 15,000 gal | 400 lb | 11 |
| 20,000 gal | 534 lb | 14 |
| 25,000 gal | 667 lb | 17 |
How much one bag raises salt
| Pool size | ppm per 40-lb bag |
|---|---|
| 10,000 gal | 480 ppm |
| 15,000 gal | 320 ppm |
| 20,000 gal | 240 ppm |
| 25,000 gal | 192 ppm |
Use this table to correct small gaps. If you are 400 ppm short in a 20,000 gallon pool, two bags overshoots slightly, while one bag falls short.
How to prepare and dose
- Know your volume. Use the pool gallons calculator for rectangles or the round pool calculator for circles.
- Test first. Use fresh water readings from the middle of the pool, not near a return.
- Add with the pump running. Pour salt around the shallow end and brush it toward the main drain.
- Wait before retesting. Circulate for about 24 hours.
- Add in steps if unsure. Under-dosing is easy to fix. Over-dosing is not.
Common mistakes
- Trusting a guessed volume. A 10 percent error in gallons means a 10 percent error in salt.
- Adding the full target without testing. Fill water and leftover salt from earlier doses may already contribute some.
- Using the wrong product. Check that the bag says it is for pools, with no additives you do not want.
- Dumping salt in one pile. A heap on the floor can stain plaster and takes much longer to dissolve.
- Chasing a low reading too soon. Salt takes time to mix, so wait before adding more.
Keeping the level steady
Making chlorine does not use up the salt. Salt leaves only with the water, through splash-out, backwashing, and overflow. Refilling with fresh water dilutes what remains.
Say you drain and replace 750 gallons, which is 5 percent of a 15,000 gallon pool. Salt drops by 5 percent, from 3,200 to 3,040 ppm. Restoring 160 ppm takes 160 ÷ 1,000,000 × 15,000 × 8.34 = 20 lb. That is half a bag.
Related calculators
Keep the rest of your chemistry in range with the pool chlorine calculator. For above-ground installations, the above ground pool calculator gives you the gallons to enter here.
Frequently asked questions
What salt level should a saltwater pool be?
Many salt chlorine generators run best between about 2,700 and 3,400 ppm, with 3,200 ppm a common target. Check your generator's manual, because running below its range makes weak chlorine and running above it can trigger a high-salt fault or speed up corrosion.
How much salt do I add?
Multiply the gap between current and target ppm by your gallons and by the weight of a gallon of water: pounds = (target − current) ÷ 1,000,000 × gallons × 8.34. To raise 15,000 gallons by 1,000 ppm takes about 125 lb.
How do I find my current salt level?
Use a salt test strip, a digital salt meter, or your generator's display. A new or freshly filled pool reads near zero, so you add the full target amount. Always test before adding, because overshooting means draining and refilling to correct.
What kind of salt do I use?
Pool-grade sodium chloride, at least 99 percent pure, sold in 40-pound bags. Avoid products with additives, and check the label for anti-caking agents, which can cloud the water in some pools.
How long until I can test after adding salt?
Broadcast the salt over the pool with the pump running, brush any that settles, and wait about 24 hours of circulation before retesting. Salt dissolves and mixes slowly, so an early reading will be misleadingly low.
Do I need to account for water that is added later?
Yes. Topping up with fresh water dilutes salt, and rain does the same, so you may need small top-up doses over the season. Splash-out and backwashing remove salt along with the water, so retest whenever a lot of water leaves the pool.
Estimates only. Verify quantities with your supplier before purchasing.