mg/L · ppm · grains per gallon
Water Hardness Converter
Convert common hardness units and classify the result using U.S. Geological Survey ranges.
USGS classification
| Classification | mg/L as CaCO₃ | Approx. gpg |
|---|---|---|
| Soft | 0–60 | 0–3.5 |
| Moderately hard | 61–120 | 3.6–7.0 |
| Hard | 121–180 | 7.1–10.5 |
| Very hard | More than 180 | More than 10.5 |