How the estimate works
Daily grain load = people × softened gallons per person per day × hardness in gpg. Penn State Extension uses 75 gallons per person per day in its example sizing calculation. We then apply your target interval plus a 20% planning reserve and round up to a common nominal capacity band.
Why this is not a final model recommendation
Nominal “32,000 grain” or “48,000 grain” labels can overstate usable capacity at efficient salt settings. Check actual manufacturer capacity, salt dose, service flow and pressure drop.
Method note. These calculators are for planning. Product selection still needs manufacturer service-flow, pressure-drop, certified performance, plumbing and local-code checks.