Starting estimates only. Always recheck hardness and your valve manual.
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People × daily use × hardness (gpg) → rough grain capacity. Optional iron adjustment.
Starting point—not a guarantee. Iron and peak flow change needs. Plumbing cuts may require a licensed plumber.
Convert gpg ↔ ppm (1 gpg ≈ 17.1 ppm as CaCO₃) before you size.
Step 1
Get a hardness reading in gpg (or convert from ppm).
Step 2
Know what the number means before you size.
Step 3
Capacity is one input—features and install still matter.