EstimatorKitFree pool salt calculator
Bags of pool salt, and where those bags land you
Enter the pool’s gallons, the salt reading off a strip and the target from your chlorinator’s plate, and this returns the pounds needed and the whole bags to buy at 83.4 lb per 1,000 ppm per 10,000 gallons. It also prints the number no other salt calculator shows you: the ppm those whole bags actually reach, which is always past the target, because salt is the one pool reading with no reverse gear. When the reading is already too high the only treatment is water, so the tool sizes that swap in gallons instead.
- 100% free
- No signup
- 40 lb bags
- Cell ranges built in
- Overshoot shown first
From the 2,700–3,400 ppm operating range printed for the AquaRite, ideal 3,200.
The number every line below is a fraction of. Work it out on the pool volume calculator rather than trusting the size on the box.
Take the reading from a strip or a meter dipped in the pool, not from the number on the cell’s display — that one is inferred from how much current the plates draw, which moves with water temperature and with how scaled the plates are.
Yours, from the store you are standing in — this site ships no price list. At 99.8% purity the bag weight and the salt weight are the same number to within a rounding error, so nothing here corrects for it.
Buy 40 lb bags
4 bags
- Salt the gap needs
- 133 lb
- Exact bags
- 3.34
- One ppm costs
- 0.17 lb
Rate: 83.4 lb is the weight of salt that makes 1,000 ppm in 10,000 gallons. That is arithmetic on the definition of a part per million, not a figure off a chart, so it holds for any pool of any shape.
Add short, then retest
4 bags is 160 lb, which lands the pool at 3,359 ppm, past the 3,200 ppm you asked for. Put in 3 first and you are at 3,119 ppm, already inside the range the cell will run on. Twenty-four hours of circulation, a fresh strip, and then the last bag if it is still wanted.
What 250 gallons of lost water does
Replacing 250 of the pool’s 20,000 gallons with fresh water takes the reading from 2,400 ppm to 2,370 ppm, a drop of 30 — and putting it back costs 5 lb. Evaporation is the exception that trips people up: water that leaves as vapor leaves the salt behind, so the reading rises in a heatwave and returns to where it was the moment you top the pool up.
Purity: the minimum purity pool salt is bagged at — evaporated or solar sodium chloride, sold as pool, food or feed grade, 99.8% or better. It varies with grade: water-softener pellets and rock salt run lower and may carry an anti-caking or rust-inhibiting additive. For scale, average salinity of open ocean water is 35,000 ppm, so the sea is about 11 times saltier than this pool at 3,200 ppm.
How to work out how much salt a pool needs
The arithmetic is one line. Everything worth getting right lives in the last step, where a whole-bag rounding decision costs either one more trip or a partial drain.
Start from gallons, not from the size on the box
Every figure here is a fraction of the volume, so a pool entered 10% large is salted 10% heavy and stays that way until enough water leaves to fix it. An above-ground pool holds less than its wall height implies and an in-ground pool holds less than its shallow-and-deep average implies, which is why the volume is worked out separately rather than guessed at here.
Test the water, then set the target off the cell's own plate
Dip a salt strip or a digital meter in the pool at elbow depth away from a return. The chlorinator's own salt display is not a second opinion — it infers salinity from the current the plates draw, so a cold spring pool reads low on the same water that reads fine in July, and scale on the plates pushes it lower again. Then pick the target from the range printed on the unit rather than from a number you remember.
Add the whole bags short, circulate a day, retest, then finish
The tool shows the ppm the rounded-up bag count reaches and the ppm one bag fewer reaches. Take the smaller one first: broadcast it over the deep end with the pump running, brush what settles on the floor so it does not sit against the plaster, leave it a full 24 hours, and retest before opening the last bag. Overshooting costs a partial drain; undershooting costs one more trip.
Technical specifications
| Dose rate | 83.4 lb of salt per 1,000 ppm per 10,000 gallons — derived from what a part per million weighs, so it holds for any pool of any shape |
|---|---|
| Bag size | 40 lb by default; editable for the 25 lb and 50 lb bags some brands use |
| Cell targets | Hayward AquaRite 2,700–3,400 ppm (ideal 3,200), Pentair IntelliChlor 3,000–4,500 ppm (ideal 3,400), or a target you type off your own plate |
| Whole-bag landing | The ppm the rounded-up count reaches and the ppm one bag fewer reaches, both printed before you buy |
| Downward move | Water swap only: the share of the pool to replace is 1 − target ÷ current reading |
| Water-loss panel | Any number of gallons replaced with fresh, converted to the ppm lost and the pounds to put it back |
| Salt purity | 99.8% sodium chloride or better, which is inside the resolution of a test strip and so is not corrected for |
| Stored or sent | Nothing — no readings, no volume, no account |
Frequently asked questions
How much salt does a 20,000 gallon pool need?
133 lb to go from 2,400 ppm to 3,200 ppm, which is 3.34 forty-pound bags. That is where the whole-bag problem starts: four bags is 160 lb and lands the pool at 3,359 ppm, past the target and only 41 ppm under the top of the range a Hayward cell will run in. Three bags is 120 lb and lands at 3,119 ppm, comfortably inside the same range, so the sensible order is four bags and the sensible first addition is three.
Can I lower the salt level without draining the pool?
No. Nothing sold for pools removes chloride — it is not consumed, it does not precipitate out, and it passes straight through sand, cartridge and DE filters alike. The only lever is replacement, and the arithmetic is proportional: swapping a fifth of the water takes a fifth of the salt with it, so a pool sitting at 4,200 ppm that wants 3,200 needs 24% of its volume out and back, which on 20,000 gallons is 4,762 gallons. Where water restrictions make that impossible, mobile reverse-osmosis trucks will filter the pool in place for a fee, which is a service call rather than a calculation.
Why does my salt reading drop after heavy rain?
Because rain dilutes the pool twice, and only the second one is permanent. The rain itself adds fresh water to a fixed quantity of salt, so the ppm falls while the water line is high; if that water later evaporates, the reading climbs back to exactly where it was. What does not come back is anything you pump off to bring the level down to the skimmer, because that water leaves with its share of the salt in it. The same distinction explains backwashing: the pounds are gone the moment the waste line runs, and the tool prices that loss in bags.
Is water softener salt the same as pool salt?
Chemically yes, commercially not always, and the difference is in what else is in the bag. Both are sodium chloride at 99.8% or better, but softener products are sold in several forms and some carry an anti-caking or iron-removal additive that has no business in a pool: iron sequestrants stain, and yellow additives color plaster. Pellets and crystals also dissolve far more slowly than the fine pool grade, so they sit on the floor for days and read low on the strip while they do it. Read the bag for two things — 99.8% NaCl or better, and no additives — and the price difference stops mattering.
How long after adding salt do I test it?
A full 24 hours with the pump running before the reading means anything. Salt dissolves quickly in warm water and slowly in a spring pool, and until it has circulated the sample you take is of a pocket rather than the pool. Two handling rules go with it: never pour salt into the skimmer, because a slug of concentrated brine through the pump, the heater and the cell is exactly what corrodes them, and brush anything that settles on the floor into suspension rather than leaving it against the plaster.
Do I have to add salt every year?
Only to replace water you lost, because the cell does not consume salt. Electrolysis splits chloride into hypochlorous acid, that sanitizes the water, and it reverts to chloride — the same atoms go round again indefinitely. So a pool that is covered, does not leak and is not backwashed hard can go a whole season without a bag, while one on a sand filter with a busy diving board needs several. Whatever the season took out, it took out as water: count the gallons rather than the months.
Does a saltwater pool taste like the sea?
Not close — a pool at 3,200 ppm is about an eleventh as salty as the ocean at 35,000 ppm. It sits near the threshold where most people can just detect salt in water, which is why it registers as faintly soft rather than as brine, and it is well under the roughly 9,000 ppm of human tears, which is the comparison that matters to anyone who opens their eyes underwater.
About salt, the cell, and the reading that only water moves
A salt chlorinator does not sanitize with salt. It sanitizes with chlorine, which it makes on the spot: water carrying dissolved sodium chloride passes between charged plates, chloride is oxidized to hypochlorous acid, that does the work, and within minutes it has reverted to chloride and is back in the pool waiting to go round again. Salt is therefore a reservoir rather than a consumable, and that single fact explains everything odd about the reading. It does not fall because the cell ran, or because August was hot, or because the pool was busy. It falls only when water physically leaves — a backwash to waste, a winter cover pumped off, a leak, a hard weekend of splash-out — and it rises when water leaves as vapor, because evaporation takes the water and leaves every pound of the salt behind. Top the pool up after a heatwave and you are back to the number you started with.
The dose itself is not a trade figure and does not need a chart: a part per million is one milligram per liter, 10,000 US gallons is 37,854 liters, so 1,000 ppm is 83.4 lb of salt and that holds for any pool of any shape. What is worth arguing about is the target, and the honest answer is that there is no site-wide one. A Hayward cell asks for 2,700–3,400 ppm and a Pentair for 3,000–4,500, so a reading that is dead center on one is a low-salt fault on the other, and either way the plate on the unit outranks anything written here. Under the range, a cell produces less chlorine and works harder doing it; over it, you get corrosion of ladders and rails, and on many units a high-salt shutdown. Because the trip in one direction is a bag and the trip in the other is a drain, this page deliberately shows the smaller bag count first. Everything downstream of the number — chlorine, pH, alkalinity, stabilizer — belongs to the pool chemical calculator, which doses per 10,000 gallons the same way.
Two practical notes that come up every season. The first is the volume: get it from the pool volume calculator rather than from the box the liner came in, because a shallow-and-deep average overstates a real in-ground floor and the error is baked into every dose you ever calculate. The second is where the water goes when you do have to dilute. Backwash and splash-out from a salt pool are not irrigation: at 3,200 ppm the run-off is well past what most turf and ornamentals tolerate season after season, so it wants routing to a sewer connection or a sacrificial area rather than onto the lawn or into the beds — and where the planting beside the deck already suffers from it, soil in a box off the ground is a different problem with its own arithmetic on the raised bed soil calculator. While you are pricing the season, the barrier around the water is usually the other line on the same invoice; the fence calculator counts the posts, rails and concrete for it.
Your readings stay in the tab
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
Salt readings, volumes and the price you paid for a bag are typed, used and dropped. Nothing is kept between visits, so the tool cannot tell you what your pool read last month — that is what the log taped inside the pump-house door is for.