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    Converting Water Hardness Values

    December 28, 2023 1 min read

    Water hardness can be expressed a number of different ways, and it's often important to know how to convert one unit to another for the purposes of selecting and properly programming water softeners. Here are the common ways water hardness is expressed and how to convert values in one unit to another:

    Common Water Hardness Units:

    mg/L - this is commonly encountered on lab reports

    ppm - also seen on lab reports and is exactly the same as mg/L

    GPG - "grains per gallon" often used by retailers and equipment manufacturers

    To convert from mg/L or ppm to GPG divide the hardness value by 17.1

    Here  are examples:

    200 mg/L / 17.1 = 11.7 GPG

    450 ppm / 17.1 = 26.3 GPG


    To convert from GPG to mg/L or ppm, multiply the hardness value by 17.1

    Here's an example:

    15 GPG x 17.1 = 256.5 mg/L (or ppm)