Water Hardness Converter
Convert water hardness between ppm, mg/L, gpg, dGH, mmol/L, and Clark degrees instantly.
Type in any field — the others update instantly.
Water hardness conversions use ppm (mg/L CaCO3) as the base unit.
Unit definitions (all relative to ppm CaCO3):
- 1 ppm = 1 mg/L CaCO3 (these are identical)
- 1 gpg (grains per gallon) = 17.118 ppm
- 1 dGH (German degrees) = 17.848 ppm
- 1 mmol/L = 100.09 ppm (molar mass of CaCO3)
- 1 Clark degree (English degrees) = 14.254 ppm
- 1 French degree (°fH) = 10 ppm
Water hardness scale (ppm):
- Soft: 0-60 ppm
- Moderately hard: 61-120 ppm
- Hard: 121-180 ppm
- Very hard: 180+ ppm
Common uses:
- Aquariums: dGH is the standard measure
- US water reports: ppm or gpg
- European water reports: dGH or French degrees
- Water softeners: gpg is most common in the US