mmol/L to PPM — water hardness converter
Some labs report hardness in millimoles per litre (mmol/L); one mmol/L of calcium carbonate hardness equals its molar mass, 100.087 mg/L, and mg/L equals ppm — so to convert mmol/L to ppm you multiply by 100.087. For example, 1.5 mmol/L × 100.087 = 150 ppm, which is hard water.
Some labs report hardness in millimoles per litre; US reports use ppm.
Convert mmol/L to ppm
Enter a number to convert; the result shows its band and how it ranks among 2,977 US counties.
Chart
mmol/L to ppm chart
| mmol/L | ppm | Band |
|---|---|---|
| 0.25 | 25 | Soft |
| 0.5 | 50 | Soft |
| 0.75 | 75 | Moderately hard |
| 1 | 100 | Moderately hard |
| 1.25 | 125 | Hard |
| 1.5 | 150 | Hard |
| 2 | 200 | Very hard |
| 2.5 | 250 | Very hard |
| 3 | 300 | Very hard |
| 4 | 400 | Very hard |
| 5 | 500 | Very hard |
Formula
The formula, and why
ppm = mmol/L × 100.087. One millimole of calcium carbonate hardness weighs its molar mass, 100.087 mg, so 1 mmol/L = 100.087 mg/L (= ppm).
ppm→gpg · gpg→ppm · °dH→ppm · all-units calculator
Questions
Frequently asked
- How many ppm is 1 mmol/L?
- 100.09 ppm — one millimole per litre of hardness equals its molar mass, 100.087 mg/L.
- Is mmol/L the same as °fH?
- Close but not identical: 1 mmol/L ≈ 10 °fH, since 1 °fH = 10 mg/L.
- What is 2 mmol/L in ppm?
- 2 × 100.087 = 200 ppm, which is very hard.
By Marko Visic, MPharm, BSc Physics. Source: Conversion factors per USGS/NIST unit definitions; band data from USGS/EPA WQP. Data last verified . Methodology.