Water hardness calculator
Convert water hardness between mmol/L, mg/L as CaCO₃, German °dH, French °fH and English °e, and grade it as soft, moderately hard, hard or very hard by °dH: 1 mmol/L CaCO₃ = 5.6 °dH and 1 °dH = 17.848 mg/L CaCO₃.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Hardness conversion
Four units plus the hardness grade.
Enter a hardness value to convert it
°dH: 0 · mg/L: 0 · mmol/L: 0
What this tool does
- Read a lab report: labs report mmol/L while appliance manuals use °dH — align them in one step.
- Set up a water softener: regeneration cycles and salt use are computed from °dH.
- Judge scaling risk for boilers and espresso machines and decide whether to soften.
Example
Input
250
Output
250 mg/L 的硬度： 以 CaCO₃ 计：250 mg/L = 2.497752 mmol/L 德国度：14.007172 °dH 法国度：25 °fH 英国度（克拉克）：17.482517 °e 分级：硬水（14–21 °dH） 换算关系：1 mmol/L CaCO₃ = 100.09 mg/L = 5.607911 °dH；1 °dH = 17.848 mg/L CaCO₃
2 mmol/L as CaCO₃ equals 200.18 mg/L and 11.216 °dH — moderately hard water.
Frequently asked questions
How much is 1 mmol/L in °dH?
As CaCO₃: 1 mmol/L = 100.09 mg/L and 1 °dH = 17.848 mg/L, so 1 mmol/L ≈ 5.6 °dH. That is the factor to apply when folding molar concentration into German degrees.
Are mg/L and ppm the same?
In water analysis they normally are: 1 mg/L = 1 ppm by mass. But ppm is sometimes quoted as CaCO₃ equivalent and sometimes as calcium itself — a factor of 2.5 apart (100.09 vs 40.08 g/mol), so confirm the convention.
Where does the grading come from?
From the German detergent regulation and WHO practice: below 8.4 °dH soft, 8.4–14 moderately hard, 14–21 hard, 21 and above very hard. Chinese drinking-water standards only cap total hardness at 450 mg/L as CaCO₃ without grading.
How do French and English degrees differ?
French °fH is 10 mg/L CaCO₃, German °dH is 10 mg/L CaO (= 17.848 mg/L CaCO₃) and English °e (Clark) is 1 grain per UK gallon ≈ 14.3 mg/L CaCO₃. All three are kept because appliance manuals differ by country.
Is hard water unhealthy?
Hardness is mostly about taste and scaling; WHO sets no health-based guideline. Water at 200–300 mg/L tastes dry and clouds tea, but calcium and magnesium are essential minerals — the real cost is scale in appliances and pipes.
Keywords：水的硬度water hardness德国度°dHCaCO₃ mg/L硬水软水mmol/L水质检测