Convert a water-hardness test result into the units used by coffee-machine manuals and filter charts. Enter total hardness as calcium carbonate (CaCO3) or a degree reading; a TDS meter reading is not a hardness measurement.
Water Hardness Converter
ppm is numerically approximately equal to mg/L for dilute water when both describe the same substance, here CaCO3. US grains per gallon and imperial grains per gallon are different. Values are rounded for display.
Conversion factors
| Unit | Equivalent in mg/L as CaCO3 |
|---|---|
| 1 ppm as CaCO3 | about 1 |
| 1 °dH | 17.848 |
| 1 °fH | 10 |
| 1 US grain/gallon | 17.118 |
The descriptive hardness band uses the USGS classification: 0–60 soft, above 60–120 moderately hard, above 120–180 hard and above 180 mg/L very hard. Local water suppliers may use other labels. Always set the machine’s hardness setting according to its own test-strip scale.
Sources: USGS water hardness guide, USGS grains-per-gallon conversion, Hoval unit conversion table.
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