PPM to °dH — water hardness converter
Water reports in ppm (equal to mg/L), while European charts use the German degree (°dH); since 1 °dH = 17.848 mg/L, converting ppm to °dH means dividing by 17.848. For example, 200 ppm ÷ 17.848 = 11.2 °dH, which is very hard water. Divide by 17.848, not 17.1.
Reading a US ppm number against a European chart means converting to the German degree (°dH).
Convert ppm to °dH
Enter a number to convert; the result shows its band and how it ranks among 2,977 US counties.
Chart
ppm to °dH chart
| ppm | °dH | Band |
|---|---|---|
| 10 | 0.6 | Soft |
| 25 | 1.4 | Soft |
| 50 | 2.8 | Soft |
| 100 | 5.6 | Moderately hard |
| 120 | 6.7 | Hard |
| 150 | 8.4 | Hard |
| 200 | 11.2 | Very hard |
| 250 | 14 | Very hard |
| 300 | 16.8 | Very hard |
| 400 | 22.4 | Very hard |
| 500 | 28 | Very hard |
| 750 | 42 | Very hard |
| 1000 | 56 | Very hard |
Formula
The formula, and why
°dH = ppm ÷ 17.848. One German degree (°dH) is defined as 10 mg/L of calcium oxide (CaO); converting to calcium carbonate by molar mass, 10 × (100.087 ÷ 56.077) = 17.848 mg/L per °dH.
Reverse: °dH to PPM · ppm→gpg · gpg→ppm · gpg→°dH · all-units calculator
Questions
Frequently asked
- How many °dH is 100 ppm?
- 100 ÷ 17.848 = 5.6 °dH, which is moderately hard.
- Is ppm the same as mg/L here?
- Yes — ppm and mg/L are identical, so the same division applies.
- What is 300 ppm in °dH?
- 300 ÷ 17.848 = 16.8 °dH, 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.