Pool Salt Calculator

Pounds, 40 lb bags, or kg from your three numbers — with the chemistry behind every digit, sourced from APHA Standard Methods, the CRC Handbook, and the three biggest SWG manufacturers' own manuals.

Your salt system says LOW SALT. The pool store chart says seven bags. Your neighbor says five.

Here's the thing — they're both guessing. The right answer depends on three numbers, and one of them (your current salt level) is almost never zero, even in a brand-new fill.

Here's the deal: give this calculator your pool volume, your current salt reading, and your generator's target. You'll get the exact pounds, the number of 40 lb bags, and a smarter add-80%-then-retest plan. You'll also see the actual chemistry — including why salt never wears out, and why your system lies to you every spring.

What you'll give us

Three inputs in: pool volume, current salt ppm, and your target. The diagram below shows each, plus where they hang off the salt generator's plumbing.

You give us: volume + current salt + target ppm. You get:pounds, bags, kg, an "add 80% first" plan — or, if you're over, exactly how much water to swap.

The calculator

Pick your generator brand for the target preset, type the rest, hit calculate. Defaults match worked example 1 — change them to match your pool, or run the defaults first to see what the result panel looks like.

Calculate your pool's salt

Three numbers in, exact pounds (and bags) out — plus an 80%-first plan, because salt is easy to add and miserable to remove.

Don't know your gallons? Pool volume calculator — two minutes, any shape, deep-links straight back here.

Why salt never wears out

Your generator doesn't consume salt — it borrows it. Electrolysis turns chloride into chlorine; the chlorine sanitizes the water; the spent chlorine reverts to chloride; the loop closes.

The only way salt leaves your pool is inside water that leaves your pool: splash-out, backwash, a leak, an overflow. Evaporation doesn't count — water vapor leaves the salt behind, which is why a hot dry August can quietly make your salt reading drift up.

Practical consequence:if your salt is dropping fast, you don't have a chemistry problem — you have a water-loss problem. Find the leak or the splashy kid before adding another bag.

Salt isn't consumed — it's borrowed. Chloride goes in to the cell, comes out as the chlorine that sanitizes the water, then reverts to chloride. The only side-exits are the orange arrows: water leaving the pool. Evaporation doesn't count — water vapor leaves the salt behind, which is why a hot dry August can quietly drift your salt reading up.

Why your "current salt" is never zero

Every gallon of liquid chlorine you've ever added left salt behind — twice. The hypochlorite itself reverts to chloride after it sanitizes (about 0.82 ppm of salt per ppm of free chlorine), and commercial bleach carries roughly an equal mole of manufacturing salt with it (another 0.83).

Call it 1.65 ppm of permanent salt per ppm of chlorine dosed. A pool that's eaten bleach for five summers can sit at 500–1,000+ ppm before the first salt bag goes in.

Moral:test first, never assume zero. The biggest dosing error on the salt-conversion subreddit is "the calculator said X bags so I bought X bags" — when the pool was already halfway to target from years of liquid-chlorine residue.

Stoichiometry: NaOCl → NaCl gives 58.44 / 70.9 = 0.824 ppm salt per ppm FC-as-Cl₂; chlor-alkali manufacturing carries roughly 1:1 molar residual NaCl. The 1.65figure is the source-of-truth used across PoolSolver's chemistry pages.

Worked examples for common salt scenarios

Eight scenarios, eight precomputed answers. Run any of them through the calculator above to see the math identical, step for step.

Example 1

How much salt for a 10,000 gallon pool (fresh fill to 3,200 ppm)

10,000 gal, current 0 ppm (verified fresh fill), target 3,200 ppm (Hayward AquaRite optimum).

267 lb

6.7 bags → buy 7. First pass (80%): 214 lb ≈ 5.3 bags.

The most-quoted scenario on the internet, with the math finally visible: 3,200 × 10,000 × 8.345×10⁻⁶ = 267 lb. Round up to seven 40 lb bags; the 80% pass leaves you a margin for the cold-water under-read.

Example 2

Salt calculator for a 15,000 gallon pool reading 2,400 ppm

15,000 gal, current 2,400 ppm, target 3,200 ppm. Δ = 800 ppm.

100 lb

2.5 bags. First pass (80%): 80 lb = 2 bags exactly.

Spring top-up reality: you almost never need the "fresh fill" dose. Two bags now, retest in 24 hours, top up only if the strip says so.

Example 3

How many bags of salt for a 20,000 gallon pool?

20,000 gal, current 0 ppm, target 3,200 ppm.

534 lb

13.4 bags → buy 14. First pass (80%): 427 lb = 10.7 bags ≈ 11.

At this size the 80% rule earns its keep — buy 14, add 11 first, and bag #14 might never leave the garage. Salt is easy to add and miserable to remove.

Example 4

Intex salt water pool calculator (12 ft round example)

1,833 gal (cylinder math from the volume page, E7) at full geometric volume — Intex's own 90%-fill convention rates the 12×30 Metal Frame at 1,718 gal (CS2110 manual p.7). Current 0 ppm, target 3,000 ppm (Intex preset).

46 lb

Using the cylinder-math 1,833 gal figure. 1.15 bags @ 40 lb. Using Intex's 1,718 gal you'd be at ~43 lb — about 6% less.

Small water is unforgiving — half a bag too much puts you 1,300 ppm over your 3,000 ppm Intex target. Weigh, don't eyeball; this is one pool size where the difference between the geometric figure and the 90%-fill figure actually matters.

Example 5

How to lower salt in a pool (over-salted fix)

25,000 gal at 4,800 ppm, target 3,400 ppm.

29.2% water swap

Replace fraction = 1 − (3,400 / 4,800) = 0.292 → 7,292 gal out, then refill with fresh water.

That's a serious water bill — every dollar of it preventable by following the 80% rule on the dosing side. Sodium chloride is non-volatile and there is no chemistry that removes it.

From 4,800 ppm to 3,400 ppm: the only knob is water. Drain 1 − (3,400 / 4,800) = 29.2% of the pool — 7,292 gal — refill with fresh water, circulate, retest. That's a real water bill (see the fill-cost calculator); a chronically over-salted pool is the strongest argument for the "add 80% first" rule on the dosing side.

Example 6

Pool salt calculator in kg (50,000 litre metric example)

50 m³ (50,000 L) pool, current 0 ppm, target 3,200 ppm.

160 kg

3.2 g/L × 50 m³ = 160 kg. 6.4 × 25 kg bags.

In SI the formula is almost embarrassingly clean — ppm IS grams per cubic metre, no 8.345 conversion factor to remember.

Example 7

Pool says low salt after winter? Read this before adding

18,000 gal at 58 °F, system claims 2,100 ppm but an independent warm-water test says 2,700 ppm. Target 3,200 ppm → Δ from test = 500 ppm.

75 lb

1.9 bags ≈ 2 — dosed off the test, not the readout.

Conductivity falls ~2%/°C (CRC); an uncompensated cell in 58 °F water reads ~20% low vs a warm-water test. Pentair itself rates its sensor at ±500 ppm (manual p.11) — one more reason the independent test wins.

Example 8

Converting a pool to salt water: the first salt dose

16,000 gal pool that's used liquid chlorine for five summers, tested current 600 ppm (per the chlorinated-salt sidebar above), target 3,200 ppm. Δ = 2,600 ppm.

347 lb

8.7 bags → buy 9.

Testing first saved this owner about two bags vs the assume-zero chart.

Why your system says LOW SALT every spring

Conductivity in salt water falls about 2% per °C as the water cools (CRC Handbook of Chemistry and Physics). Salt-cell readouts work by measuring conductivity. So as the water cools, the readout drops — even though the salt didn't go anywhere.

Add the manufacturer's honesty (Pentair rates its own sensor at ±500 ppm, manual p.11) and the math gets brutal: a March opening at 58 °F can show 600–800 ppm below the same pool tested in July, with no chemistry actually changing.

Practical rule:never dose salt off a cold-water LED. Test with a strip or a handheld TDS meter at room-temperature, dose to that, and let the cell's display catch up to reality as the water warms.

Two readings, one pool, one batch of salt. Ionic conductivity falls about 2% per °C (CRC Handbook); the cell's conductivity-based readout falls with it. At 58 °F your SWG can under-read by 20%+ versus the same water tested at summer temperatures — the "LOW SALT" alarm in March is almost never a salt problem. Dose to a test strip, not the LED.

None of the SWG manuals in our files documents this readout-temperature link directly. The claim rests on standard electrochemistry (CRC) plus the manufacturer-published sensor-accuracy spec.

Six pools, one straight line

Bags scale linearly with volume — there's no diminishing-returns curve, no shape adjustment, no chemistry shortcut. The chart below maps a fresh-fill to 3,200 ppm across pools from 5,000 to 30,000 gallons.

Six pool sizes, fresh fill from 0 to 3,200 ppm. Bags scale linearly with volume — a 20,000 gal pool needs exactly 4× what a 5,000 gal pool needs, no exceptions. If your current salt is above zero (and it almost always is — see the "why your salt is never zero" sidebar), you need less.

Reference tables

Two tables you can cite directly. Both released under CC BY 4.0 — reuse them with a link back.

T1 · Salt needed (lb / 40 lb bags) by pool volume and Δppm

All values derived from the master formula: lb = Δppm × gallons × 8.345×10⁻⁶ (Standard Methods + CRC water density).

Pool volume	Δ500 ppm	Δ1,000 ppm	Δ2,000 ppm	Δ3,200 ppm
5,000 gal	21 lb· 0.5 bag	42 lb· 1.0 bag	83 lb· 2.1 bag	134 lb· 3.3 bag
10,000 gal	42 lb· 1.0 bag	83 lb· 2.1 bag	167 lb· 4.2 bag	267 lb· 6.7 bag
15,000 gal	63 lb· 1.6 bag	125 lb· 3.1 bag	250 lb· 6.3 bag	401 lb· 10.0 bag
20,000 gal	83 lb· 2.1 bag	167 lb· 4.2 bag	334 lb· 8.3 bag	534 lb· 13.4 bag
25,000 gal	104 lb· 2.6 bag	209 lb· 5.2 bag	417 lb· 10.4 bag	668 lb· 16.7 bag
30,000 gal	125 lb· 3.1 bag	250 lb· 6.3 bag	501 lb· 12.5 bag	801 lb· 20.0 bag

A 10,000 gal pool needs exactly 4× what a 2,500 gal Intex needs — dosing is linear in volume, no exceptions.

T2 · SWG brand target ranges (from each manufacturer's own manual)

Three brands, three different ideal targets. Rows ship as each manual is verified — anything not here is not yet sourced.

Brand · Model	Ideal	Optimum range	Operating bounds	Sensor note	Source
IntexKrystal Clear CS2110	3,000 ppm	2,500–3,500 ppm	<2,000 ppm trouble code 91; salty taste begins 3,500–4,000 ppm	not specified	CS2110 manual p.5–6
HaywardAquaRite	3,200 ppm	2,700–3,400 ppm	<2,700 ppm efficiency drops; salty taste begins ~3,500–4,000 ppm	not specified	AquaRite manual p.5
PentairIntelliChlor IC15/IC20/IC40/IC60	3,600 ppm	3,600–4,500 ppm	<2,600 ppm unit shuts off; >4,500 ppm corrosion warning	±500 ppm	IntelliChlor manual p.10–11

Note the 600 ppm spread between Intex's 3,000 and Pentair's 3,600. There is no industry-wide target — match your own equipment.

Methodology & sources

The dosing math rests on two facts: parts per million is milligrams of solute per kilogram of water (the convention in Standard Methods for the Examination of Water and Wastewater, APHA), and a US gallon of pool water weighs 8.345 pounds at 60 °F (CRC Handbook). Multiply those and the whole calculator collapses to one line of arithmetic — derived in full above, not copied from a chart.

Target salinity ranges come exclusively from manufacturer installation manuals, cited by model and page in T2. Where we don't have a manual on file, the brand simply isn't listed. The salt-loop chemistry is textbook chlor-alkali electrochemistry; the cold-water readout effect follows from the ~2%-per-°C temperature dependence of ionic conductivity in the CRC tables.

The 1.65 ppm-of-salt-per-ppm-of-FC residual from liquid chlorine combines a 0.824 stoichiometric coefficient (NaOCl → NaCl, 58.44/70.9) with a ~0.83 chlor-alkali manufacturing-residual factor. That number is the source-of-truth for every chemistry page on PoolSolver — it lives once, in lib/dosing/core.ts, and is imported by every page that cites it.

Sources used on this page

Standard Methods for the Examination of Water and Wastewater (APHA)— the analytical-chemistry convention that ppm = mg solute / kg water, on which every dosing calculation on the site rests.
CRC Handbook of Chemistry and Physics— water density (8.345 lb/gal at 60 °F) and the temperature dependence of ionic conductivity (~2%/°C for aqueous NaCl).
NIST SP 811— exact gallon-to-litre conversion (1 US gal = 3.785411784 L) used in every unit cascade.
Hayward AquaRite Electronic Chlorine Generator manual— salt range and ideal (p. 5), salt-type purity and prohibited types (p. 5), add-salt protocol (p. 5).
Pentair IntelliChlor IC15/IC20/IC40/IC60 manual (P/N 520589 Rev. R)— the optimum-conditions table (p. 10), the operating bounds + sensor accuracy spec (p. 11), and the explicit "never add salt through the skimmer or surge tank" instruction (p. 13).
Intex Krystal Clear Saltwater System CS2110 manual— salt range and ideal (p. 5–6), and the cross-cited 90%-fill pool-capacity table that we use on the volume page's 12 ft Intex example (p. 7).
Chlor-alkali electrochemistry (textbook) — the closed-loop sanitation chain (Cl⁻ → Cl₂ → HOCl → Cl⁻) and the basis for the 1.65 ppm-of-salt-per-ppm-of-FC residual.

Reference tables T1 and T2 above are released under CC BY 4.0. Reuse them anywhere — just attribute PoolSolver and link back.

Frequently asked questions

How much salt do I need for a 10,000 gallon pool?

For a fresh fill to 3,200 ppm: 267 lb, about 6.7 forty-pound bags (round up to seven). The math is one line: 3,200 × 10,000 × 8.345×10⁻⁶ = 267. If your current salt is above zero (which is the usual case — see the chlorinated-salt sidebar), the number drops linearly.

What should my pool's salt level be?

There is no universal number. Three of the biggest SWG brands aim for three different targets — Intex 3,000 ppm, Hayward 3,200 ppm, Pentair 3,600 ppm. The cell's own manual is the only authority; the brand chips above give the preset for the three brands we've verified.

Can I use water softener salt in my pool?

Only if it's ≥99% pure sodium chloride with zero additives. Both Hayward (manual p. 5) and Pentair (manual p. 11) accept water-softener salt as long as there's no anti-caking agent (sodium ferrocyanide / yellow prussiate of soda), no iodine, and no rock salt. Pentair additionally bans calcium chloride and potassium chloride as substitutes.

How long after adding salt can I turn on the generator?

About 24 hours. Both Hayward (manual p. 5) and Pentair (manual p. 13) specify 24 hours of circulation before turning the cell on or trusting the displayed salt reading. Brush the bottom to break up piles; never add salt through the skimmer or surge tank (Pentair p. 13).

Does pool salt evaporate or get used up?

No to both. The generator borrows chloride to make chlorine; the chlorine sanitizes and reverts to chloride; loop closes. Evaporation removes water but leaves the salt behind, which is why a hot August can actually drift your reading up. The only way salt leaves is inside water that leaves — splash-out, backwash, leaks, overflow.

Why does my system say low salt in spring?

Conductivity falls about 2% per °C as water cools (CRC Handbook). Salt cells measure conductivity, so the reading drops with temperature even though the salt didn't go anywhere. Pentair rates its own sensor at ±500 ppm (manual p. 11); add a 20 °C spring/summer swing and a cold-water LOW SALT alarm is almost never a salt problem. Test with a strip at room temperature, dose to that.

How do I lower the salt level?

Only by replacing water. Drain a fraction = 1 − (target ÷ current) of the pool, refill, circulate, retest. For a 25,000 gal pool at 4,800 ppm aiming for 3,400, that's 29.2% = 7,292 gal— see worked example 5 above. That's a real water bill — the strongest argument for the "add 80% first" rule on the dosing side.

How often do I need to add salt?

Only after water-loss events: backwash, splash-out, leaks, big rains with overflow. Salt isn't consumed by chlorination and doesn't evaporate. If you're reaching for a bag monthly with no obvious water loss, the calculator can't help you — find the leak.

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Next in Pool Chemistry: Salt Chlorine Generator Calculator.

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