Free pool tool
Pool Salt Calculator
Enter your pool volume, your current salt reading and the level your chlorine generator needs, and the calculator works out how many pounds and bags of salt to add. If the salt is too high, it tells you how much of the water to replace instead.
Not sure? Work out your pool volume.
From a salt test strip or meter. A new pool with no salt is 0.
Most chlorine generators want 2,700 to 3,400 ppm. Check the cell's manual.
Add pool salt
87.6 lb
- Use pool salt: 99% pure sodium chloride with no anti-caking agents or iodine.
- Turn the chlorine generator off, pour the salt into the shallow end, and brush it until it dissolves so it does not sit on the floor.
- Run the pump for 24 hours before turning the generator back on and re-testing. Strips read low until the salt has fully mixed.
- Add less than the full amount if you are unsure of your volume. Salt is easy to add and only comes out by draining.
How it works
Salt Is Measured in Parts per Million of the Water
A salt reading of 3,200 ppm means every million pounds of water carries 3,200 pounds of salt. A gallon of water weighs about 8.345 pounds, so the salt a pool needs is the rise in ppm times the weight of the water, divided by a million. In metric units it is simpler again, because one ppm in water is one milligram per litre.
Salt (g) = ppm increase × litres ÷ 1,000
That works out to about 8.3 lb of salt for every 100 ppm in 10,000 gallons, which is a handy figure to keep in your head when you are standing next to a pallet of bags.
Worked example
15,000 Gallons, From 2,500 to 3,200 ppm
The salt needs to rise by 700 ppm. Multiplying 700 by 15,000 gallons and by 8.345 pounds per gallon, then dividing by a million, gives about 87.6 lb of salt, or 2.2 bags of 40 lb. In metric terms the pool holds about 56,800 litres, and 700 × 56,800 ÷ 1,000 gives about 39.7 kg.
Two bags would bring this pool to about 3,140 ppm, which is inside most cells' range and leaves room to top up later. Because salt only comes out by draining, rounding down is the safer choice when the pool's volume is an estimate.
Getting it right
Read the Cell, Then Read the Water
Start with the target. Salt chlorine generators are built for a specific range, and the manual or the label on the control box gives it. The calculator defaults to 3,200 ppm because it sits in the middle of the most common range, but a cell designed for a lower level needs the lower number.
Then make sure the reading you start from is real. Turn the generator off, pour the salt into the shallow end, and brush it until it dissolves so it doesn't sit on the floor. Run the pump for 24 hours before testing again, because strips and meters both read low until the salt has fully mixed. The guide to saltwater pool maintenance covers cell cleaning and the chemistry that changes when a pool runs on salt.
Too much salt
The Only Way Down Is Fresh Water
Salt doesn't evaporate, get used up or filter out, so a pool that is over its target stays there until some of the water is replaced. The share to replace is the excess divided by the current reading, assuming the fill water has almost no salt in it.
Lowering 4,000 ppm to 3,200 ppm means replacing about 20% of the water. Before draining, check the cell's manual, since most tolerate a few hundred ppm above their ideal level. Salt is also the best way to confirm a pool's volume: if a measured dose moves the reading further than the calculator predicts, the pool is smaller than you thought, and the pool volume calculator is worth a second look.
For pool service companies
The same maths runs at every stop in Pool Runs
These calculators use the dosing and saturation-index formulas built into the Pool Runs technician app. A tech logs the readings at the pool, the app works out the doses for that pool's own volume, and the visit lands in the customer's service history and report without anyone typing it up later.
- Readings and doses saved against each pool, with the saturation index for every visit
- A mobile app that works offline in a backyard with no signal
- Chemicals and parts tracked on every truck and in the shop
Try Pool Runs free
Free for 30 days, month to month, with white-glove onboarding to move your customers in.
Questions
Pool Salt Calculator FAQ
More free tools
Related pool calculators
Pool Volume Calculator
Work out how many gallons or litres a rectangular, round, oval or kidney pool holds from its size and depth.
Open the calculatorPool Chemical Calculator
Enter your readings and targets, and get every dose in the order to add it, with the saturation index before and after.
Open the calculatorLSI Calculator
Calculate the Langelier saturation index with the cyanuric acid correction, then set targets to see the new index and the doses to get there.
Open the calculator