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Convert water-hardness units while keeping the limits of the result clear.

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Water hardness unit converter

Compare a hardness result in milligrams per liter (as CaCO₃) with grains per US gallon. This is a unit conversion, not a system-sizing recommendation.

120 mg/L ≈ 7.02 gpg

Uses the approximate factor 1 gpg = 17.1 mg/L as CaCO₃. For dilute water, ppm is approximately mg/L. A hardness result does not establish drinking-water safety.

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Use the converter below when one result is in mg/L as calcium carbonate and another is in grains per US gallon. Divide mg/L by about 17.1 to get grains per gallon, or multiply grains per gallon by 17.1 to go the other way.

The tool runs in your browser and doesn’t send its input to us. It converts units rather than choosing a softener or judging water safety.

Before entering a result, check the sample point and test method. A reading after a softener isn’t the incoming hardness used in a sizing discussion.

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