This table shows water hardness only in metric units (ppm or its equivalent of mg/L). Some water analysis labs, particularly in the US may report hardness in terms of grains per gallon. You can convert from ppm to gpg by dividing ppm by 17.1
| Term | ppm (mg/L) |
| Soft | Less than 20 |
| Slightly Hard | 20.0 - 60.0 |
| Moderately Hard | 60.0 - 120.0 |
| Hard | 120.0 - 180.0 |
| Very Hard | 180.0 and over |