How much salt to convert a 20,000-gallon pool?

About 534 lb to reach 3,200 ppm from zero: 20,000 × 3,200 × 8.34 × 10⁻⁶ ≈ 533.8 lb, roughly thirteen 40-lb bags. Subtract any existing salinity your test shows.

Do I have to drain my pool to convert to salt?

Usually no. You keep the existing water, balance it, add the generator, and dissolve salt up to the target ppm. Draining is only needed if the water is unbalanced beyond correction or already too salty.

Is a saltwater pool chlorine-free?

No. The generator produces chlorine from the salt, so a salt pool is a chlorine pool with an automatic chlorine source. You still maintain free chlorine, pH, CYA and occasional shocking.

How salty does the water feel?

At about 3,200 ppm the water is roughly one-tenth as salty as the ocean — most swimmers describe it as soft rather than salty, and it is gentler on eyes and skin than a heavily hand-chlorinated pool.

How to convert a pool to saltwater: how much salt you need

Switching a traditional pool to a salt system is mostly about one calculation: how much salt to add to fresh water to reach your generator’s target.

By Francesco Zinghinì

Safety: dosing figures are estimates. Follow the product label, add one chemical at a time, never mix pool chemicals, add chemical to water (never water to chemical), keep chemicals away from children, and re-test before swimming. Add about ¾ of a dose, re-test, then top up. Not a substitute for professional pool service.

Converting to saltwater does not mean draining and refilling. In most cases you keep the water you have, add a salt chlorine generator, and dissolve enough salt to bring an essentially salt-free pool up to the generator’s target — commonly around 3,200 ppm. The generator then makes chlorine from that salt continuously, so you stop buying and dosing chlorine by hand.

The conversion formula

A fresh chlorine pool reads close to 0 ppm salt, so the “add” is the whole target:

pounds of salt ≈ gallons × target ppm × 8.34 × 10⁻⁶

This is the general salt formula with a current reading of zero. If your test shows some existing salinity (chlorine and other additives contribute a little), subtract it from the target first so you do not overshoot.

Worked example

15,000-gallon pool, target 3,200 ppm from zero:

15,000 × 3,200 × 8.34 × 10⁻⁶ = 400.3 lb — roughly ten 40-lb bags of pool salt.

Because the target scales linearly with volume, a 20,000-gallon pool at the same 3,200 ppm needs about 534 lb, and a 10,000-gallon pool needs about 267 lb. Always round down a little and top up after testing — adding salt is easy, removing it means draining.

Step by step

Balance the water first. Get pH, total alkalinity, cyanuric acid and calcium hardness into range before you start; salt does not fix chemistry, it only replaces the chlorine source.
Install the generator (or have it installed) per its manual, plumbed after the filter and heater.
Test current salinity and compute the gap to target.
Add salt with the pump running, brushing it around so it dissolves; wait a full circulation cycle (often 24 hours).
Re-test and fine-tune, then set the generator’s output so it holds your free chlorine.

What the switch does — and does not — change

A salt pool is not a chlorine-free pool. The generator makes chlorine on site by electrolyzing the salt, so you still keep free chlorine in range; you just automate the dosing. Salinity at ~3,200 ppm is roughly a tenth of seawater, so the water feels soft rather than salty. You still need to watch pH (salt generators tend to push pH up over time), maintain cyanuric acid to protect the chlorine from sunlight, and occasionally shock the pool.

Salt itself is not used up — you top it up mainly to replace splash-out, backwash and dilution from rain and refills, so after the initial charge a salt pool needs only small, infrequent additions.

Sizing the salt system to your pool

The generator itself is rated by pool size, and matching it matters as much as the salt charge. A cell rated for, say, 15,000 gallons will struggle to keep up on a 25,000-gallon pool, running near 100% output and wearing out sooner. Sizing the generator above your pool volume lets it hold chlorine at a lower duty cycle, which extends cell life and gives you headroom for heat waves and heavy bather loads. Salt cells are consumable — they gradually lose output over several seasons — so buy the capacity once and run it easy.

Is your pool a good candidate?

Most pools convert happily, but a few materials warrant care. Continuous low-level salinity can be hard on some natural-stone coping, unsealed masonry and certain metal fittings or older heaters. None of this rules out salt — millions of pools run on it — but it is worth sealing porous stone, checking that heater and fixture metals are salt-rated, and keeping the water balanced so it is neither corrosive nor scaling. Because a salt generator tends to raise pH over time, plan on periodic small acid additions to hold pH in range. Get these basics right up front and a converted pool is lower-effort than hand-dosing chlorine for years afterward.

The bottom line

Converting to salt is mostly a one-time calculation followed by years of easier maintenance. Keep the water you have, balance it, add a correctly sized generator, and dissolve enough pool salt to reach the target ppm from a near-zero start — for a typical mid-size pool that is a few hundred pounds, scaling directly with volume. Round down and top up after testing so you do not overshoot, because lowering salinity means draining. Remember what does not change: you still keep free chlorine, pH and cyanuric acid in range, and you still shock occasionally; the generator simply automates the chlorine you used to add by hand. Seal porous stone, confirm your metals are salt-rated, and plan on small periodic acid additions to counter the generator’s upward pull on pH.

Size your initial charge with the salt conversion tool, dial in later adjustments with the salt calculator, and correct an over-salted pool with the salinity tool.