Water Hardness Calculator
Calculate total water hardness from calcium and magnesium levels. Get results in mg/L, ppm, grains per gallon, mmol/L, French degrees, German degrees, and a clear hardness classification.
How the water hardness calculator works
This calculator uses the standard formula to compute total hardness as calcium carbonate (CaCO₃) equivalent: Total Hardness (mg/L) = 2.497 × Ca (mg/L) + 4.118 × Mg (mg/L). It then converts the result into multiple units: ppm (same as mg/L), grains per gallon (gpg), mmol/L, French degrees (°f), and German degrees (°dH). The result is also classified as Soft, Moderately Hard, Hard, or Very Hard according to standard water quality guidelines.
Enter your calcium and magnesium concentrations below, or toggle to enter total hardness directly. Choose your preferred unit for the main result, and the calculator will show all conversions instantly.
Step 1: Water Parameters
Understanding Water Hardness
Hardness is primarily caused by dissolved calcium and magnesium. The total hardness as CaCO₃ equivalent is the standard measure used worldwide for water quality reporting and appliance protection.
Step 2: Unit Preferences
Hardness Classifications
Soft 0–60 mg/L · Moderately Hard 61–120 mg/L · Hard 121–180 mg/L · Very Hard >180 mg/L (as CaCO₃).
Hardness Results
Total Hardness
All Unit Conversions
| Unit | Value | Description |
|---|
Hardness Breakdown
Formula & Conversion Factors
Total Hardness (mg/L as CaCO₃) = 2.497 × Ca + 4.118 × Mg
Conversions: 1 mg/L = 1 ppm · 1 gpg = 17.1 mg/L · 1 mmol/L = 100.1 mg/L · 1 °f = 10 mg/L · 1 °dH = 17.9 mg/L
Frequently Asked Questions
What is water hardness?
Water hardness is a measure of dissolved calcium and magnesium ions in water. It is typically expressed as mg/L or ppm of calcium carbonate (CaCO₃) equivalent.
How is water hardness calculated?
Total hardness (as CaCO₃) = 2.497 × Ca (mg/L) + 4.118 × Mg (mg/L). This gives the equivalent concentration of calcium carbonate in mg/L.
What are the hardness classifications?
Soft: 0–60 mg/L, Moderately Hard: 61–120 mg/L, Hard: 121–180 mg/L, Very Hard: >180 mg/L (as CaCO₃).
How do I convert mg/L to grains per gallon?
Divide the mg/L value by 17.1. For example, 171 mg/L ÷ 17.1 = 10 grains per gallon (gpg).
What is the difference between temporary and permanent hardness?
Temporary hardness is caused by dissolved bicarbonate minerals and can be removed by boiling. Permanent hardness is caused by sulfate or chloride compounds and cannot be removed by boiling.
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