Water Hardness as CaCO₃ Calculator

Convert between common water hardness units (ppm, mg/L, gpg, °dH) and express total hardness as calcium carbonate equivalent (CaCO₃). For students, lab technicians, and water treatment professionals. All calculations run offline in your browser.

Note: Educational and planning tool only. Follow your lab SOPs, safety data sheets (SDS), and water quality regulations.

Input Parameters

Hardness Value

Accepts numbers, decimals (dot or comma), and scientific notation (1e-3).

Input Unit

Result Precision

Hardness Results

Primary Result

150.000 ppm as CaCO₃

Total hardness expressed as calcium carbonate equivalent.

Equivalent Values

Unit	Value

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Quick Unit Swap

→

8.758 gpg

Updates instantly as you type or change units.

Understanding Water Hardness

Water hardness is primarily caused by dissolved calcium and magnesium ions. Expressing hardness as CaCO₃ equivalent provides a standardized metric for comparison and treatment planning, regardless of the original ion ratios.

How to Use This Tool

Enter your measured hardness value (from test strips, titration, or ICP analysis).
Select the unit of your input value.
Click "Calculate Hardness" to see all equivalent values.
Use the quick conversion strip for frequent unit swaps.

Example Calculations

Scenario	Input (Unit)	Result (ppm CaCO₃)
Moderately hard water	12.5 gpg	214.0 ppm
Calcium concentration	40 mg/L Ca²⁺	99.8 ppm
German standard	8.4 °dH	150.0 ppm

Common Unit Conversions

Unit	Abbreviation	Conversion to ppm CaCO₃
Grains per Gallon	gpg	1 gpg = 17.118 ppm
German Degree	°dH	1 °dH = 17.848 ppm
French Degree	°fH	1 °fH = 10.0 ppm
mg/L Ca²⁺	mg/L Ca	1 mg/L Ca = 2.497 ppm
mg/L Mg²⁺	mg/L Mg	1 mg/L Mg = 4.118 ppm

Common Mistakes & Pitfalls

Confusing ppm as CaCO₃ with ppm of individual ions.
Assuming 1:1 ratio of calcium to magnesium when converting.
Not accounting for temperature effects on titration results.
Using inappropriate conversion factors for very soft or very hard water.

Frequently Asked Questions

Q: What is the difference between temporary and permanent hardness?

Temporary hardness is caused by bicarbonates and can be removed by boiling. Permanent hardness is caused by sulfates/chlorides and requires ion exchange or chemical softening.

Q: Why use CaCO₃ as a reference standard?

Calcium carbonate provides a consistent molar mass (100.0869 g/mol) and allows comparison of different ion contributions on an equivalent basis.

Q: How accurate are these conversions for extreme water compositions?

Conversions assume ideal ionic behavior. For very high TDS (>1000 ppm) or unusual ion ratios, direct measurement via titration is recommended.

Q: What measurement method gives the most reliable input?

Titration (EDTA method) is the standard laboratory technique. Test strips are convenient but less precise. Always calibrate instruments regularly.

Formulas & Assumptions

Primary formula: ppm CaCO₃ = (Input value) × (Unit-specific conversion factor)

Molar mass constants: CaCO₃ = 100.0869 g/mol, Ca = 40.078 g/mol, Mg = 24.305 g/mol

Unit factors: 1 gpg = 17.118 ppm, 1 °dH = 17.848 ppm, 1 °fH = 10.0 ppm

Ion conversions: ppm CaCO₃ = (mg/L Ca) × (100.0869/40.078) ≈ 2.497

Rounding: Results rounded to selected decimal places using symmetric rounding (half away from zero).

Assumption: All hardness is from Ca²⁺ and Mg²⁺; other divalent cations are negligible.

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Water Hardness as CaCO3 Calculator

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