Water Hardness Calculator
From PPM (mg/L)
ppm (mg/L)
From GPG (Grains per Gallon)
gpg
Formula
1 gpg = 17.1 ppm | Soft < 60 ppm | Moderate 60–120 | Hard 120–180 | Very Hard > 180
Frequently Asked Questions
What is water hardness?
Water hardness measures the concentration of dissolved minerals, primarily calcium and magnesium. It's expressed in ppm (parts per million, same as mg/L) or gpg (grains per gallon). 1 gpg = 17.1 ppm.
What is considered hard water?
Soft: <60 ppm (<3.5 gpg). Moderately hard: 60–120 ppm (3.5–7.0 gpg). Hard: 120–180 ppm (7.0–10.5 gpg). Very hard: >180 ppm (>10.5 gpg).
Do I need a water softener?
If your water is above 7 gpg (120 ppm), a softener can extend appliance life, reduce soap usage, and prevent scale. Below that level, it's generally optional.
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