Salt Chlorine Generator Size Calculator
A 20,000-gallon pool that uses 2 ppm of chlorine a day needs its salt cell to make about 0.33 lb (151 g) of chlorine a day. A cell rated for 1.5 lb a day at 100% makes that in 5.3 hours, or at a 67% output setting over 8 hours of pump time.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (7 sections)
Size a salt chlorine generator by the chlorine your pool uses, then check that the cell can make it in the hours your pump runs. The pool size printed on the box is a second check, not the main one.
About these numbers. The cell output (1.5 lb a day) and the box rating (40,000 gallons) in the calculator are example values, not any brand's specs. Use the numbers from the cell you are looking at. How much chlorine your pool uses per day is the key input: measure it by testing free chlorine (FC) in the evening and again the next evening without adding chlorine in between.
Calculator: pounds of chlorine per day
Chlorine needed (lb a day) = ppm used per day × gallons × 3.785 ÷ 453,592. That is the same as "ppm × gallons" converted to pounds. With the example values:
- Chlorine your pool needs: 0.33 lb a day (151 g), for 20,000 gallons losing 2 ppm a day.
- Cell run time at 100% output: 5.3 hours a day for a cell that makes 1.5 lb a day.
- Output setting for 8 hours of pump time: 67%, which leaves room to turn it up.
- Box rating vs your pool: 2.0 times your volume.
Cells are often listed by pounds of chlorine a day or grams per hour. If yours lists grams per hour, multiply by 24 to get grams a day, then divide by 453.6 and enter the result as pounds.
Box ratings vs real chlorine demand
The pool size on the box assumes ideal conditions. Hayward's AquaRite manual lists three models by pool size: AQR3 for pools up to 15,000 gallons, AQR9 up to 25,000 gallons, and AQR15 up to 40,000 gallons. The same manual says the chlorine a pool actually needs varies with the number of swimmers (bather load), rainfall, temperature, and how clean the pool is.
That is why sizing by pounds a day is more reliable. A pool in full sun, in hot weather, with a lot of swimmers can use much more chlorine than the same pool in spring. A cell rated for more gallons than your pool:
- reaches the chlorine you need in fewer hours, so it can keep up in a heat wave;
- runs at a lower output setting most of the time;
- costs more to buy and to replace.
We could not confirm a published rule for how much bigger the cell should be. Use the calculator with your summer chlorine use: if the output setting it shows is near 100% for your pump hours, look at a larger cell.
Run hours and the output setting
A salt cell makes chlorine only while water flows through it. So the cell's real daily output = its rated output per hour × the share of time it is on × the pump hours. The calculator shows the hours at 100% and the output setting that spreads them over your pump schedule. Hayward's manual suggests starting the output setting at about 50%, testing chlorine, and adjusting.
If you want to run the pump fewer hours, for example with a variable-speed pump, check the output setting again. A cell that needs 100% for 8 hours can't keep up on a 6-hour schedule. The pump run time calculator helps you plan the hours.
Chlorine target and stabilizer for salt pools
A salt pool needs stabilizer (cyanuric acid, CYA) to keep the sun from burning off chlorine, and its free chlorine target depends on that CYA. At CYA 70 ppm, our engine's target for a salt pool is 3.5–5.5 ppm FC, with 3.5 ppm as the minimum. See pool chlorine levels for other CYA levels.
Salt level matters too. Hayward's AquaRite manual lists 2,700–3,400 ppm as ideal, with 3,200 ppm best. A low salt level cuts chlorine output. Check your own cell's manual, then use the pool salt calculator to reach the level it lists. For day-to-day care, see salt water pool care and salt cell cleaning. Thinking of switching? Start with salt water pool conversion.
Salt cells on above-ground pools
Salt systems are sold for above-ground pools too, usually as a separate unit or combined with the filter pump. One example is the Intex Krystal Clear saltwater system CG-26663, which Intex lists for above-ground pools up to 4,500 gallons and for filter pumps with a flow of 300 to 1,000 gallons per hour. The same sizing logic applies: check the pounds or grams a day against what your pool uses.
Before you add salt to any pool, check the pool maker's manual to see whether salt water is allowed with its walls and metal parts. We could not confirm one rule that covers all above-ground pools. Salt can also affect what is around the pool: Hayward's manual, for example, says to ask a stone specialist before using a salt system next to natural stone coping or decking.
Electrical safety. Salt cells and their power supplies run on household current near water. Use the GFCI-protected plug or circuit the maker requires. The U.S. Consumer Product Safety Commission (CPSC) recommends GFCIs on pool equipment and an electrician qualified in pool and spa work for wiring. Hire a licensed electrician for any hard-wired unit.
FAQ
What size salt cell do I need?
One that makes your pool's daily chlorine in fewer hours than your pump runs. A 20,000-gallon pool using 2 ppm a day needs about 0.33 lb a day. A cell that makes 1.5 lb a day covers that at 67% output over 8 pump hours.
How many gallons can a salt cell handle?
The box gives the maker's figure. Hayward, for example, lists its AquaRite models for pools up to 15,000, 25,000, and 40,000 gallons. Those ratings assume ideal conditions. Check the pounds a day against your pool's real chlorine use.
Should I buy a salt cell rated for a bigger pool?
Often yes, if the calculator shows your output setting near 100% in summer. A larger cell reaches your chlorine target in fewer hours and runs at a lower setting. The trade-off is a higher price for the cell and its replacement.
Can you put a salt system on an above ground pool?
Yes, if the pool maker allows salt water. Salt systems for above-ground pools exist, such as Intex's CG-26663 for pools up to 4,500 gallons. Check your pool's manual first, and size the cell by the chlorine your pool uses.
Sources
- Hayward, AquaRite owner's manual 092538 Rev D (model sizes, what changes chlorine demand, ideal salt, start at 50% output): hayward.com (PDF)
- Intex, Krystal Clear saltwater system CG-26663 (pools up to 4,500 gallons, pumps 300–1,000 gph): intexcorp.com
- U.S. CPSC, Don't swim with shocks (GFCI on pool equipment, qualified electrician): cpsc.gov
- Free chlorine targets by CYA and unit conversions: methodology