Hardness unit converter
Convert water hardness between mg/L as CaCO3, German degrees, French degrees, grains per gallon and meq/L, with a soft-to-very-hard classification.
Results
| mg/L as CaCO3 (ppm) | 120 |
|---|---|
| German degrees (°dH) | 6.72 |
| French degrees (°f) | 12 |
| Grains per US gallon (gpg) | 7.01 |
| meq/L | 2.398 |
At 120 mg/L as CaCO3 this water classifies as hard. Expect scale on heating elements, geysers and RO membranes. Softening (or antiscalant dosing ahead of RO) is the standard response. Size a softener on measured hardness and real daily consumption, with a volumetric valve so regeneration follows actual use.
Formula used
1 °dH = 17.848 mg/L as CaCO3
1 °f = 10 mg/L as CaCO3
1 gpg (US) = 17.118 mg/L as CaCO3
1 meq/L = 50.045 mg/L as CaCO3
- °dH
- German degrees of hardness
- °f
- French degrees of hardness
- gpg
- grains per US gallon
- meq/L
- milliequivalents per litre
All conversions run through mg/L as CaCO3 as the common basis. Classification bands used: soft < 60, moderately hard 60–120, hard 120–180, very hard > 180 mg/L as CaCO3, following the WHO convention. Other sources place the boundaries a little differently, so treat a value near a boundary as being in both bands rather than as a decided classification.
The background
- Water hardness: what it is and how it is measuredHardness is dissolved calcium and magnesium, the minerals behind scale in geysers, kettles and membranes. The units are the confusing part; the chemistry is simple.
- Softener sizing basics: hardness load, resin volume and salt doseSizing a softener is bookkeeping: hardness in, capacity held, salt spent. Three numbers and two checks produce a defensible selection.
- Scaling indices (LSI and RSI) in plain languageThe Langelier and Ryznar indices condense pH, hardness, alkalinity, temperature and TDS into one number that predicts whether water will deposit calcium carbonate or dissolve it. It answers a scaling question and does not give a corrosion rate.
Equipment for this duty
Send the water analysis and duty point, and the branch confirms exact selections, pricing and lead times, usually within one working day.
Request a quoteResults are indicative engineering estimates based on standard formulas and typical assumptions. They are not a design service; confirm any design against a full water analysis and the relevant manufacturer’s data.