GPG to °dH — water hardness converter
Grains per gallon (gpg) is the US hardness unit; the German degree (°dH) is common in Europe. Since 1 gpg = 17.118 mg/L and 1 °dH = 17.848 mg/L, converting gpg to °dH means multiplying by about 0.959. For example, 10 gpg = 9.6 °dH, which is hard water.
Grains per gallon is the US unit; the German degree (°dH) is common in Europe — the two are close in size.
Convert gpg to °dH
Enter a number to convert; the result shows its band and how it ranks among 2,977 US counties.
Chart
gpg to °dH chart
| gpg | °dH | Band |
|---|---|---|
| 1 | 1 | Soft |
| 2 | 1.9 | Soft |
| 3 | 2.9 | Soft |
| 5 | 4.8 | Moderately hard |
| 7 | 6.7 | Moderately hard |
| 10 | 9.6 | Hard |
| 12 | 11.5 | Very hard |
| 15 | 14.4 | Very hard |
| 20 | 19.2 | Very hard |
| 25 | 24 | Very hard |
| 30 | 28.8 | Very hard |
Formula
The formula, and why
°dH = gpg × (17.118 ÷ 17.848) = gpg × 0.959. 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.
ppm→gpg · gpg→ppm · mg/L→gpg · all-units calculator
Questions
Frequently asked
- How many °dH is 1 gpg?
- About 0.96 °dH — the two units are within roughly 4% of each other.
- Are gpg and °dH close in size?
- Yes, unusually close: 1 gpg = 0.959 °dH, because their base mg/L values are similar.
- What is 20 gpg in °dH?
- 20 × 0.959 = 19.2 °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.