Water hardness is reported in different units depending on your test kit, water utility report, or country. This tool converts between all common units and rates your water for coffee machine use.
| Unit | Name | 1 unit = | Common In |
|---|---|---|---|
| ppm / mg/L | Parts per million (as CaCO₃) | 0.058 GPG | US municipal reports, most test strips |
| GPG | Grains per gallon | 17.12 ppm | US water softeners, some test kits |
| °dH | German degrees | 17.85 ppm | European appliance manuals, German reports |
| °fH | French degrees | 10 ppm | French, Swiss, Belgian reports |
| mg/L Ca²⁺ | Calcium ion concentration | ≈2.5 ppm CaCO₃ | Lab water analysis |
| GPG | ppm | Rating | Descaling Frequency |
|---|---|---|---|
| 0–3.5 | 0–60 | Soft — ideal for pod machines | Every 4–6 months |
| 3.5–7 | 60–120 | Moderate — suitable for all machines | Every 2–3 months |
| 7–10.5 | 120–180 | Hard — filter recommended | Every 6–8 weeks |
| 10.5–14 | 180–240 | Very Hard — filter required | Every 3–4 weeks |
| 14+ | 240+ | Extreme — inline softener recommended | Every 2 weeks |
Use your GPG value in the Descaling Schedule Calculator for a precise maintenance interval based on your machine type and brew frequency.
Conversion factors are based on standard CaCO₃ equivalents. Lab water analysis reports may use different baseline compounds — verify the measurement basis if values seem unexpected.