Water Hardness Calculator

Calculate Water Hardness in All Major Units

Enter your water sample's calcium and magnesium concentrations or total hardness to determine water hardness in mg/L (ppm), mmol/L, °dH, °fH, and °e. Useful for water quality, chemistry, aquariums, and more.

Water Hardness Calculator Examples

See how to use the Water Hardness Calculator with real-world scenarios.

Tap Water (Ions Method)

Calcium & Magnesium

Calculate water hardness for tap water with 40 mg/L Ca²⁺ and 12 mg/L Mg²⁺, result in mg/L.

Calculation Method: Calcium & Magnesium

Calcium (mg/L): 40 mg/L

Magnesium (mg/L): 12 mg/L

Result Unit: mg/L

Aquarium Water (mmol/L)

Calcium & Magnesium

Calculate water hardness for aquarium water: 25 mg/L Ca²⁺, 8 mg/L Mg²⁺, result in mmol/L.

Calculation Method: Calcium & Magnesium

Calcium (mg/L): 25 mg/L

Magnesium (mg/L): 8 mg/L

Result Unit: mmol/L

Well Water (Total Hardness)

Total Hardness

Convert total hardness 180 mg/L CaCO₃ to °dH.

Calculation Method: Total Hardness

Total Hardness (mg/L as CaCO₃): 180 mg/L

Result Unit: °dH

Softened Water (French Degrees)

Total Hardness

Convert total hardness 60 mg/L CaCO₃ to °fH.

Calculation Method: Total Hardness

Total Hardness (mg/L as CaCO₃): 60 mg/L

Result Unit: °fH

Other Titles
Understanding Water Hardness: A Comprehensive Guide
Everything you need to know about water hardness, its calculation, and real-world applications.

What is Water Hardness?

  • Definition of Water Hardness
  • Why Hardness Matters in Water Quality
  • Common Sources of Hardness
Water hardness refers to the concentration of dissolved calcium and magnesium ions in water. It is a key indicator of water quality in chemistry, environmental science, and industry.
Hardness and Water Use

Hardness in Everyday Water Samples

  • Tap water typically has a hardness between 60-180 mg/L as CaCO₃.
  • Soft water: <60 mg/L, Hard water: >180 mg/L.

Step-by-Step Guide to Using the Water Hardness Calculator

  • Choosing the Calculation Method
  • Entering Ion Concentrations or Total Hardness
  • Interpreting the Results
To use the Water Hardness Calculator, select your preferred calculation method: Calcium & Magnesium or Total Hardness. Enter the required values and select the result unit. The calculator will instantly provide the hardness value and the formula used.
Quick and Accurate Hardness Calculation

Sample Calculations

  • For 40 mg/L Ca²⁺ and 12 mg/L Mg²⁺, Hardness = 2.5×40 + 4.1×12 = 100 + 49.2 = 149.2 mg/L.
  • For 180 mg/L CaCO₃, °dH = 180 / 17.848 = 10.08.

Real-World Applications of Water Hardness Calculation

  • Drinking Water Safety
  • Aquarium and Industrial Uses
  • Water Softening and Treatment
Water hardness measurement is essential in many fields: ensuring safe drinking water, maintaining aquarium health, optimizing industrial processes, and setting up water softeners.
Why Hardness Matters in Practice

Hardness in Action

  • Aquarium owners monitor hardness for fish health.
  • Municipalities monitor hardness for water safety compliance.

Common Misconceptions and Correct Methods

  • Hardness vs. Softness
  • Unit Conversions
  • Hardness and Soap Efficiency
Many believe all hard water is bad, but moderate hardness is often beneficial. Unit conversions can be confusing; always use the correct formula. Hardness affects soap efficiency, but soft water can be corrosive.
Avoiding Calculation Mistakes

Misconceptions Explained

  • 1 °dH = 17.848 mg/L CaCO₃.
  • Soft water can increase pipe corrosion risk.

Mathematical Derivation and Examples

  • Hardness from Ions: The Formula
  • Hardness from Total Value
  • Unit Conversions and Practical Tips
Hardness (mg/L CaCO₃) = 2.5 × [Ca²⁺] + 4.1 × [Mg²⁺]. For conversions: mmol/L = mg/L / 100.09, °dH = mg/L / 17.848, °fH = mg/L / 10, °e = mg/L / 14.254.
Formulas and Example Calculations

Mathematical Examples

  • Ca = 25 mg/L, Mg = 8 mg/L: Hardness = 2.5×25 + 4.1×8 = 62.5 + 32.8 = 95.3 mg/L.
  • 60 mg/L CaCO₃ to °fH: 60 / 10 = 6 °fH.