Convert water hardness
Most water reports show hardness as mg/L or ppm as calcium carbonate. Water softener sizing often uses grains per gallon.
Hardness categories
| Category | mg/L or ppm | Grains per gallon |
|---|---|---|
| Soft | 0–60 | 0–3.5 |
| Moderately hard | 61–120 | 3.6–7.0 |
| Hard | 121–180 | 7.1–10.5 |
| Very hard | 181+ | 10.6+ |
What the number means
Hardness does not automatically mean water is unsafe. It usually matters because of scale buildup, spots on dishes, soap performance, and water-using appliances.
If your number is in the very hard range and you own your home, a softener sizing calculator may be a logical next step. If your concern is taste, odor, color, or a specific contaminant, start with a water quality report or a home test instead.
Sources and limitations
- USGS water hardness classification: 0–60 soft, 61–120 moderately hard, 121–180 hard, and more than 180 very hard.
- Conversion used: grains per gallon ≈ ppm ÷ 17.1.