We can express water hardness in PPMs as well as in mmol/L of CaCO3 (calcium carbonate). It is quite easy to** convert PPM to mmol/L**. We will show you *exactly* how you can calculate how many mmol/L is any amount of PPMs. On top of that, you will get these 2 free online tools that make this conversion much easier:

**PPM To mmol/L Calculator.**Here you just insert PPMs, and the calculator will automatically convert it to mmol/L of CaCO3.**PPM To mmol/L Chart.**We have converted 0-1,000 PPM to mmol/L, and summarized all the results in a neat conversion chart. In the chart, we have also color-coded water hardness categorization, namely**soft**water*(0-60 ppm)*with,*this green color***moderately hard**water*(61-120 ppm)*with this,*light blue color***hard**water*(121-180 ppm)*with, and*this blue color***very hard**water*(181+ ppm)*with.*this dark blue color*

Here is the key **PPM to mmol/L** of CaCO3 formula (* Parts Per Million* to

*):*

**m**illi**mol**per**L**iter**Water Hardness (mmol/L of CaCO3) = PPM / 100.09**

Basically, to get mmol/L, we have to divide PPMs by 100.09. Roughly speaking, 1 PPM is equal to 0.01 mmol/L of CaCO3 (we make less than 0.1% accuracy error with this approximation).

*Quick Example:* How many mmol/L of CaCO3 is 100 PPMs? Let’s use the formula above:

Water Hardness (mmol/L of CaCO3) = **100 PPM** / 100.09 = *0.999 mmol/L Of CaCO3*

We almost always use 100 PPM = 1 mmol/L of CaCO3 approximation. In the following calculator and chart, you can see that we calculate the resulting mmol/L to 2 decimal digits. You can freely use both of these tools here:

## PPM To mmol/L Of CaCO3 Calculator

Let’s say you want to convert 120 PPM to mmol/L of CaCO3. Use the PPM slider, slide it to ‘120’, and you get the result:

120 PPM is equal to **1.20 mmol/L of CaCO3**.

Here is the whole conversion chart you can consult as well:

### PPM To mmol/L Of CaCO3 Chart

PPM (Parts Per Million): |
mmol/L Of CaCO3 (Calcium Carbonate): |

0 PPM | 0 mmol/L Of CaCO3 |

1 PPM | 0.01 mmol/L Of CaCO3 |

5 PPM | 0.05 mmol/L Of CaCO3 |

10 PPM | 0.10 mmol/L Of CaCO3 |

15 PPM | 0.15 mmol/L Of CaCO3 |

20 PPM | 0.20 mmol/L Of CaCO3 |

25 PPM | 0.25 mmol/L Of CaCO3 |

30 PPM | 0.30 mmol/L Of CaCO3 |

35 PPM | 0.35 mmol/L Of CaCO3 |

40 PPM | 0.40 mmol/L Of CaCO3 |

45 PPM | 0.45 mmol/L Of CaCO3 |

50 PPM | 0.50 mmol/L Of CaCO3 |

60 PPM | 0.60 mmol/L Of CaCO3 |

70 PPM | 0.70 mmol/L Of CaCO3 |

80 PPM | 0.80 mmol/L Of CaCO3 |

90 PPM | 0.90 mmol/L Of CaCO3 |

100 PPM | 1.00 mmol/L Of CaCO3 |

110 PPM | 1.10 mmol/L Of CaCO3 |

120 PPM | 1.20 mmol/L Of CaCO3 |

130 PPM | 1.30 mmol/L Of CaCO3 |

140 PPM | 1.40 mmol/L Of CaCO3 |

150 PPM | 1.50 mmol/L Of CaCO3 |

160 PPM | 1.60 mmol/L Of CaCO3 |

170 PPM | 1.70 mmol/L Of CaCO3 |

180 PPM | 1.80 mmol/L Of CaCO3 |

190 PPM | 1.90 mmol/L Of CaCO3 |

200 PPM | 2.00 mmol/L Of CaCO3 |

250 PPM | 2.50 mmol/L Of CaCO3 |

300 PPM | 3.00 mmol/L Of CaCO3 |

350 PPM | 3.50 mmol/L Of CaCO3 |

400 PPM | 4.00 mmol/L Of CaCO3 |

450 PPM | 4.50 mmol/L Of CaCO3 |

500 PPM | 5.00 mmol/L Of CaCO3 |

550 PPM | 5.50 mmol/L Of CaCO3 |

600 PPM | 6.00 mmol/L Of CaCO3 |

650 PPM | 6.50 mmol/L Of CaCO3 |

700 PPM | 7.00 mmol/L Of CaCO3 |

750 PPM | 7.50 mmol/L Of CaCO3 |

800 PPM | 8.00 mmol/L Of CaCO3 |

850 PPM | 8.50 mmol/L Of CaCO3 |

900 PPM | 9.00 mmol/L Of CaCO3 |

950 PPM | 9.50 mmol/L Of CaCO3 |

1000 PPM | 10.00 mmol/L Of CaCO3 |

If you check the colors in this chart (or consult this water hardness PPM scale), you can see that:

contains from*Soft*water**0 to 0.60 mmol/L**of CaCO3.contains from*Moderately hard*Â water**0.61 to 1.20 mmol/L**of CaCO3.contains from*Hard*water**1.21 to 1.80 mmol/L**of CaCO3.contains more than*Very hard*Â water**1.81 mmol/L**of CaCO3.

With the calculator and this chart, you will quite easily convert PPM to mmol/L of CaCO3. If you need some help, you can use the comment section below, give us some numbers, and we can help you make the conversion.

Here are some similar calculators that might be helpful:

Please convert 138 ppm water hardness to degree (no symbol for degree) E. As in 0-8=soft, 9-10=soft ??

Hi Rebecca, you are probably referring to PPM to dH or dGH conversion (these are known as degrees of Hardness or degrees of General Hardness, also known as German degrees). We have a PPM to dGH calculator here; you can see that 138 PPM is equal to 7.73 degrees of Hardness (dH / dGH).

138 PPM or 7.73 dH is categorized as “Hard” water. Namely, water with hardness from 121 to 180 PPM (or 6.73 to 10.09 dH) is considered “Hard” water. Above that (181+ PPM or 10.10 dH) is considered “Very Hard” water, while 61 PPM to 120 PPM is considered “Moderately Hard” water. Below that, you have “Soft” water. Hope this helps.