Inputs
Advanced · Full OptionsResults
| Field | Value | Unit |
|---|---|---|
| Sample | — | — |
| Input mode | — | — |
| Hardness | — | mg/L as CaCO₃ (ppm) |
| Grains per gallon | — | gpg |
| German degrees | — | °dH |
| French degrees | — | °fH |
| English/Clark degrees | — | °e |
| Millimoles per litre | — | mmol/L (as CaCO₃) |
| Classification | — | Soft / Moderately hard / Hard / Very hard |
| Timestamp | — | Local |
Saved History
| # | Timestamp | Sample | Input mode | Input value(s) | mg/L (ppm) | gpg | °dH | °fH | °e | mmol/L | Class |
|---|
History is kept in-browser only. Export for backup.
Example Data
| Location | Hardness (mg/L as CaCO₃) | gpg | °dH | °fH | °e | mmol/L | Classification |
|---|---|---|---|---|---|---|---|
| Kitchen tap | 140 | 8.19 | 7.85 | 14.00 | 9.82 | 1.40 | Hard |
| Well water | 260 | 15.20 | 14.58 | 26.00 | 18.24 | 2.60 | Very hard |
| Rain tank | 25 | 1.46 | 1.40 | 2.50 | 1.75 | 0.25 | Soft |
| Lab feed | 60 | 3.51 | 3.36 | 6.00 | 4.21 | 0.60 | Soft |
| Boiler make-up | 110 | 6.43 | 6.17 | 11.00 | 7.72 | 1.10 | Moderately hard |
Formula used
All results are normalized to hardness as calcium carbonate equivalents (mg/L as CaCO₃), then converted to other units.
- From Ca and Mg (mg/L): Hardness as CaCO₃ (mg/L) ≈
2.497 × Ca + 4.118 × Mg - gpg → mg/L:
mg/L = gpg × 17.1 - °dH → mg/L:
mg/L = °dH × 17.848 - °fH → mg/L:
mg/L = °fH × 10 - °e → mg/L:
mg/L = °e × 14.254 - mmol/L → mg/L:
mg/L = mmol/L × 100.0869
Conversions from mg/L (as CaCO₃):
gpg = mg/L ÷ 17.1°dH = mg/L ÷ 17.848°fH = mg/L ÷ 10°e = mg/L ÷ 14.254mmol/L = mg/L ÷ 100.0869
Classification (default): Soft ≤60 · Moderately hard 61–120 · Hard 121–180 · Very hard >180 mg/L as CaCO₃.
How to use this calculator
- Choose an Input mode that matches your test result or known values.
- Enter the numeric value. For Ca and Mg, provide both concentrations in mg/L.
- Set desired Decimal precision and, if needed, enable Custom thresholds for classification.
- Click Calculate to see conversions across ppm, gpg, °dH, °fH, °e, and mmol/L with an overall classification.
- Use Add to history to store the record in your browser session.
- Click Download Results CSV/PDF or export your full history for reporting and archiving.
- Review the Formula used section for unit definitions and conversion math.
FAQs
It describes the concentration of divalent minerals—mainly calcium and magnesium. Hardness is commonly expressed as mg/L as CaCO₃, but other units like gpg, °dH, and mmol/L are also used.
Use mg/L as CaCO₃ for most reports and regulatory references. gpg is common in residential softener literature; °dH/°fH are common in Europe; mmol/L is SI-based.
Factors (2.497 for Ca; 4.118 for Mg) are standard approximations to express hardness as CaCO₃ equivalents. Actual speciation and other ions can slightly influence results.
By default, USGS thresholds: ≤60 soft, 61–120 moderately hard, 121–180 hard, >180 very hard (all in mg/L as CaCO₃). You can customize thresholds under advanced options.
Yes. Use the conversions to set dishwashers, coffee machines, or boiler treatment. Always check device manuals for preferred units.
No. It converts reported values and helps planning. For compliance or health decisions, use certified laboratory results and local guidelines.
Small differences arise from rounding and reference choices (e.g., 17.1 vs 17.12 mg/L per gpg; CaCO₃ molar mass 100.0869). This tool uses widely accepted standard values.
Note: Results are for informational purposes. Always validate against your method and reporting standards.