Water Softener Sizing Calculator

Salt-based grain capacity from household size, hardness (GPG or ppm), and optional iron — 7-day cycle with a 25% reserve

Size a residential ion-exchange water softener from the number of people, gallons per person (default 75, editable), hardness in grains per gallon or ppm, water source, and iron if you have it. The calculator reports daily grain demand, 7-day demand, capacity with a 25% reserve, and the next standard class (24,000 / 32,000 / 48,000 / 64,000 / 80,000 / 96,000 grains), plus how often that class would regenerate at 75% drawdown. Starting point only — not a water test, not a septic permit, and not a salt-free conditioner size.

How the formula works: sizing guide. Regen too often or hardness still at the tap: troubleshooting. Grain capacity vs salt-free flow rating: comparison. Household × hardness table: sizing chart. Plumbing index: plumbing calculators hub.

Hard water scales heaters and supply lines. Heater first-hour rating: water heater sizing calculator. Incoming main: water supply pipe sizing. Well that feeds the softener: well pump sizing calculator.

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How to Use This Water Softener Sizing Calculator

Enter household size and gallons per person (default 75). If you have a water bill, put indoor gallons per day in the override and the people × 75 path is ignored. Enter hardness in GPG or ppm (ppm is divided by 17.1). Pick city or well. Well water shows an iron-test note; enter iron in ppm when you have it. The tool reports daily grains, 7-day grains, capacity with a 25% reserve, and the next standard class: 24,000 / 32,000 / 48,000 / 64,000 / 80,000 / 96,000 grains, plus how often that class would regenerate at 75% drawdown.

Daily grains = gallons/day × compensated GPG
Rated capacity = daily grains × 7 × 1.25

Why 7 days and 25% exist: sizing guide. Regen every other day or hardness still at the tap: troubleshooting. Grain math does not size a salt-free conditioner: comparison. Household × hardness grid: sizing chart.

What This Number Is (and Is Not)

The headline is a grain-capacity class for a salt-based ion-exchange tank, not a flow rate and not a brine-tank gallon stamp. A family of four on 10 GPG city water, 75 gallons each, no iron, is 3,000 grains/day, 21,000/week, 26,250 with reserve — a 32,000-grain system. A 24,000-grain quote on that house omitted the reserve.

Salt-free is a different worksheet. Conditioners that do not remove hardness have no grain capacity. Size those by peak GPM. Salt-based vs salt-free.

Already regenerating every other day? Undersize, iron fouling, or a bypass left open can fake a “bad” unit.

Troubleshooting →

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