Salt Cell Sizing Calculator

Picking a salt cell is a sizing job, not a chemistry job. The industry rule of thumb is to fit a generator rated for 1.5×–2.0× the pool's gallons — oversizing on purpose so the cell runs at a relaxed 50–70% output instead of flat out. A right-sized cell lasts about 5–7 years; an undersized one running near 100% burns out in 2–3. We start at the 2.0× default and only slide toward the 1.5× floor when low-demand factors stack (shade, cool weather, light use).

oversizeFactor      = clamp(2.0 + min(0, demandScore), 1.5, 2.0)
recommendedRatedGal = poolGallons × oversizeFactor
recommendedClass    = smallest product tier ≥ recommendedRatedGal
                      [15k · 20k · 25k · 40k · 60k gal]
high demand (≥3 of 4 factors maxed) → one tier up

baselineOutput  = poolGallons / 10,000           (lb/day at 100%)
expectedRun %   = baselineOutput / (class / 10,000)  ≈ poolGallons / class

dimensions mode: poolGallons = pool-volume engine (shape × avg depth × 7.48 gal/ft³)
                 avgDepth = (shallow + deep) / 2 (deep blank ⇒ shallow)

Why two levers, not one. Low-demand conditions slide the oversize factor down toward 1.5×. High-demand conditions don't push the factor past 2.0× (the cited rule caps there) — instead they bump the recommendation up one real product tier, the way an installer steps from an IC40-class to an IC60-class cell. So a neutral 20,000-gal pool lands at the 40,000-gal class; the same pool in full sun with heavy use and water features steps up to the 60,000-gal class.

The run-% check. One pound of chlorine a day treats roughly 10,000 gallons, so a 20,000-gal pool needs about 2.0 lb/day, and a 40,000-gal-class cell (≈4.0 lb/day) covers that at about 50% output — the longevity sweet spot. The optional second panel turns a unit's published lb/day rating into the daily run hours and % setting, and flags a cell that can't keep up at the buffered target.

We snap to real product classes (15k / 20k / 25k / 40k / 60k gal), not an exact computed number, because installers buy SKUs — example references like Pentair IntelliChlor IC20/IC40/IC60 map to the 20k/40k/60k classes. This is a vendor-neutral planning aid; final selection should follow your chosen brand's sizing chart.

Sizing the cell is the middle of a three-part job. The salt the water needs before the generator will run at all is dosed on the pool salt calculator, and what to charge for the changeover itself, cell and board against your markup plus install hours, the start-up visit and the initial salt charge, is built on the salt system conversion pricing calculator. If the cell is being replaced rather than fitted for the first time, price it alongside the rest of the pad on the pool equipment replacement pricing calculator.

Sources: chlorine-generator.com — Salt chlorine generator sizing (the 1.5×–2.0× rule, bracket chart, demand factors, 50–70% longevity target); INYO Pools — How to Size a Salt Chlorine Generator (oversize-for- longevity, IC20/IC40/IC60 tiers); My Pool Calculator — Saltwater Generator Sizing (the 1 lb/day ≈ 10,000 gal baseline + 15–20% buffer).