Water Softener Size Calculator

Enter your water hardness, iron and household size to see the grain capacity you need. Not sure of your hardness? A test strip or your water utility’s annual water quality report will tell you.

Check your city's water quality report or a test strip. Don't know? Many U.S. homes fall between 7 and 15 gpg.

Common on well water. We add 4 gpg per 1 ppm of iron, a standard rule of thumb.

75 is a common sizing figure. Use more for big tubs, frequent laundry or irrigation on softened water.

Recommended size

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  • Effective hardness—
  • Grains removed per day—
  • Grains between regenerations—

We pick a size whose rated capacity is at least a third more than you need, so it can regenerate on an efficient salt setting. Rated capacities assume the maximum salt dose.

How this calculator works

Daily softening load = people × gallons per person per day × compensated hardness (grains per gallon). Each part per million of iron adds about 4 grains per gallon. We size the softener so it regenerates about once a week while running at roughly 75% of its rated capacity, which is more salt-efficient than running a resin bed to empty.

To convert hardness reported in mg/L or ppm to grains per gallon, divide by 17.1.