Pool Salt CalculatorPool Salt Calculator
Find exactly how much salt your salt water pool needs — in pounds, kilograms and bags — for any volume and target ppm. Results update as you type.
Salt to add
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Enter your pool volume to see results.
- Bags to buy
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- Exact bags
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- Pounds
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- Kilograms
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How to use the pool salt calculator
- Enter your pool volume in US gallons or litres. If you don't know it, open "Don't know your volume?" and enter your pool's shape, length, width (or diameter) and average depth. The pool volume calculator has more detail.
- Enter your current salt level in ppm (parts per million). Use 0 for a newly filled pool. For an existing pool, test the water with salt test strips, a titration kit or a digital meter — don't rely on a guess.
- Enter your target salt level. The default is 3,200 ppm, a common ideal for residential chlorine generators. Your cell manufacturer's manual lists the right range for your model.
- Pick your bag size. Pool salt in the US is most commonly sold in 40 lb bags; 20, 25 and 50 lb bags and 20 or 25 kg bags are also available.
The result card shows the total salt in both pounds and kilograms, the exact number of bags, and a rounded "bags to buy" figure. We round up so you won't come up short, except when the leftover is less than 5% of a bag (for example 10.01 bags shows as 10) — that tiny difference is far smaller than the error of any home salt test. Your inputs are saved on your device, and Copy share link gives you a URL with your numbers filled in.
Pool salt formula
Salinity is measured in parts per million (ppm) by weight: 1 ppm means 1 pound of salt per 1,000,000 pounds of water. A US gallon of water weighs about 8.34 lb, so:
Salt (lb) = Gallons × 8.34 × (Target ppm − Current ppm) ÷ 1,000,000
In metric units it's even simpler, because a litre of water weighs about 1 kg and 1 ppm equals 1 mg per litre:
Salt (kg) = Litres × (Target ppm − Current ppm) ÷ 1,000,000
Then divide by bag weight to get the number of bags. A handy shortcut: 1 lb of salt raises 1,000 gallons by about 120 ppm, and 1 kg raises 1,000 litres by 1,000 ppm.
Worked example 1: a new 15,000-gallon pool
You've just filled a 15,000-gallon pool with fresh water (0 ppm), and your generator manual says the ideal is 3,200 ppm.
- ppm increase = 3,200 − 0 = 3,200
- Salt = 15,000 × 8.34 × 3,200 ÷ 1,000,000 = 400.3 lb (181.6 kg)
- Bags = 400.3 ÷ 40 = 10.01 → 10 bags of 40 lb
Worked example 2: topping up a 20,000-gallon pool
Your test reads 2,400 ppm after a rainy month and you want to get back to 3,200 ppm.
- ppm increase = 3,200 − 2,400 = 800
- Salt = 20,000 × 8.34 × 800 ÷ 1,000,000 = 133.4 lb (60.5 kg)
- Bags = 133.4 ÷ 40 = 3.34 → buy 4 bags, but consider adding 3, waiting 24 hours and retesting before adding the rest.
Pool salt chart (lb and 40 lb bags)
Pounds of pool salt needed to raise salinity by the amount shown, for common pool sizes. Use the "+3,200 ppm" row for a freshly filled pool; for top-ups, use the row closest to the difference between your reading and your target. Values are calculated with the formula above.
| Raise by | 5,000 gal | 10,000 gal | 15,000 gal | 20,000 gal | 25,000 gal | 30,000 gal | 35,000 gal | 40,000 gal |
|---|---|---|---|---|---|---|---|---|
| +200 ppm | 8 lb 1 bag | 17 lb 1 bag | 25 lb 1 bag | 33 lb 1 bag | 42 lb 1 bag | 50 lb 2 bags | 58 lb 2 bags | 67 lb 2 bags |
| +400 ppm | 17 lb 1 bag | 33 lb 1 bag | 50 lb 2 bags | 67 lb 2 bags | 83 lb 3 bags | 100 lb 3 bags | 117 lb 3 bags | 133 lb 4 bags |
| +600 ppm | 25 lb 1 bag | 50 lb 2 bags | 75 lb 2 bags | 100 lb 3 bags | 125 lb 4 bags | 150 lb 4 bags | 175 lb 5 bags | 200 lb 5 bags |
| +800 ppm | 33 lb 1 bag | 67 lb 2 bags | 100 lb 3 bags | 133 lb 4 bags | 167 lb 5 bags | 200 lb 5 bags | 234 lb 6 bags | 267 lb 7 bags |
| +1,000 ppm | 42 lb 1 bag | 83 lb 3 bags | 125 lb 4 bags | 167 lb 5 bags | 209 lb 6 bags | 250 lb 7 bags | 292 lb 8 bags | 334 lb 9 bags |
| +1,500 ppm | 63 lb 2 bags | 125 lb 4 bags | 188 lb 5 bags | 250 lb 7 bags | 313 lb 8 bags | 375 lb 10 bags | 438 lb 11 bags | 500 lb 13 bags |
| +2,000 ppm | 83 lb 3 bags | 167 lb 5 bags | 250 lb 7 bags | 334 lb 9 bags | 417 lb 11 bags | 500 lb 13 bags | 584 lb 15 bags | 667 lb 17 bags |
| +2,500 ppm | 104 lb 3 bags | 209 lb 6 bags | 313 lb 8 bags | 417 lb 11 bags | 521 lb 13 bags | 626 lb 16 bags | 730 lb 19 bags | 834 lb 21 bags |
| +3,000 ppm | 125 lb 4 bags | 250 lb 7 bags | 375 lb 10 bags | 500 lb 13 bags | 626 lb 16 bags | 751 lb 19 bags | 876 lb 22 bags | 1,001 lb 25 bags |
| +3,200 ppm | 133 lb 4 bags | 267 lb 7 bags | 400 lb 10 bags | 534 lb 14 bags | 667 lb 17 bags | 801 lb 20 bags | 934 lb 24 bags | 1,068 lb 27 bags |
Need a version to stick on the pump-room wall? See the printable pool salt chart (gallons and litres).
How to add salt to a pool
- Test first. Measure salt with an independent test and check that pH and alkalinity are in range. Note that a generator's displayed salt is an estimate.
- Check your manual. Many manufacturers recommend turning the chlorine generator off while new salt dissolves, so undissolved salt doesn't pass through the cell.
- Run the pump. Keep the filter pump running on its normal setting so the salt mixes evenly.
- Broadcast the salt in the pool, not in the skimmer. Pour it around the shallow end and perimeter so it spreads out. Avoid dumping it all in one pile.
- Brush the floor to help piles dissolve and keep salt from sitting on plaster or vinyl.
- Wait about 24 hours with the pump running, then retest. Readings taken too early near an undissolved patch can be wildly off.
- Add the rest if needed. For big additions, adding about 75–80% of the calculated amount first and the rest after retesting is the easiest way to avoid overshooting.
Tips for accurate results
- Use pure pool salt. Look for at least 99% sodium chloride, non-iodized and without anti-caking agents. Additives and impurities can cause staining or cloudy water.
- Get the volume right. Volume is the biggest source of error. A pool listed as "15,000 gallons" may hold noticeably more or less depending on its real average depth and water level. The estimator uses standard geometry; freeform pools are best treated as an approximation.
- Overshooting costs more than undershooting. Adding salt is easy; removing it means draining water. When unsure, add a little less and top up.
- Test temperature matters. Some generators lower their readings or stop producing chlorine in cold water. Compare readings in similar conditions.
- Record your additions. Noting how much salt you added and the readings before and after helps you spot a wrong volume estimate or a drifting sensor.
Pool salt calculator FAQ
How much salt do I need for my pool?
Multiply your pool volume in gallons by 8.34, then by the ppm increase you need, and divide by 1,000,000. A 15,000-gallon pool starting from fresh water (0 ppm) and targeting 3,200 ppm needs about 400 lb of salt. If your pool already contains salt, only the difference between your current reading and your target counts, so test first.
How many bags of salt do I need for my pool?
Divide the pounds of salt by your bag size. Starting from 0 ppm and targeting 3,200 ppm, plan on roughly 2/3 of a 40 lb bag per 1,000 gallons (26.7 lb per 1,000 gallons). That works out to about 7 bags for 10,000 gallons, 10 bags for 15,000 gallons and 14 bags for 20,000 gallons. Topping up an existing salt pool usually takes only one to four bags.
How much does one 40 lb bag of salt raise the ppm?
One 40 lb bag raises salinity by about 4,796,000 ÷ gallons ppm. In practice: ~480 ppm in 10,000 gallons, ~320 ppm in 15,000 gallons, ~240 ppm in 20,000 gallons and ~160 ppm in 30,000 gallons. One pound of salt raises 1,000 gallons by about 120 ppm.
What salt level should a salt water pool be?
Most residential salt chlorine generators are designed to run somewhere around 2,700–3,400 ppm, and 3,200 ppm is a common ideal. The correct figure is the one in your cell manufacturer's manual, because different models have different ranges. For comparison, seawater is roughly 35,000 ppm, so a salt pool is only about a tenth as salty as the ocean.
What kind of salt should I use?
Use pure sodium chloride sold as pool salt: at least 99% pure, non-iodized, and free of anti-caking agents (such as yellow prussiate of soda), which can cause staining. Avoid rock salt with insoluble impurities, iodized table salt, and water-softener pellets with additives. Fine-grained or "fast-dissolving" pool salt dissolves quickest.
How long does it take salt to dissolve, and when can I swim?
With the pump running and some brushing, granular pool salt typically dissolves within a few hours; coarse salt can take longer. Wait about 24 hours of circulation before you retest so the reading reflects the whole pool. Many manufacturers recommend switching the generator off until the salt has dissolved — check your manual. Swimming is generally fine once the salt has dissolved and your chlorine level is normal.
What happens if I add too much salt?
Moderately high salt is rarely dangerous, but it can trigger a "high salt" warning or shutdown on some generators, and very high salinity is harder on metal fittings and stone. Salt does not evaporate or get used up, so the only fix is dilution: drain part of the water and refill with fresh water. Use our dilution calculator to find the percentage.
Why does my salt level keep dropping?
Salt is not consumed by chlorine generation — the chloride is recycled. It leaves only with water: splash-out, backwashing, draining, leaks, and overflow after heavy rain. Evaporation removes water but leaves salt behind, which is why topping up with fresh water after evaporation does not lower salinity.
My generator reading and test strip disagree. Which do I trust?
Neither is perfect. Generators estimate salt from the cell's electrical conductivity, which depends on water temperature and cell condition (scale buildup can affect readings). Test with an independent method — salt test strips, a titration kit, or a calibrated digital meter — before adding salt, and add in stages if the readings disagree significantly.
Does this calculator work for Pentair, Hayward and other generators?
Yes. The amount of salt needed is basic chemistry and is the same for every brand: it depends only on water volume and the ppm increase. Enter the target level from your own generator's manual. This site is independent and not affiliated with any equipment manufacturer.