Total Hardness Calculator

Calculate hardness quickly for labs, homes, and plants. Choose units, validate inputs, and track history. Download CSV or PDF reports for audits and sharing.

Calculator Inputs

Enter calcium and magnesium concentration, then compute total hardness as CaCO3.
Used in exports and history.
Recorded for context; not used in the formula.
Choose how many decimals to display.
Accepted units: mg/L, mmol/L, meq/L.
Accepted units: mg/L, mmol/L, meq/L.
Client-side hints; server still validates safely.

History (exportable)

Add calculated results, then download CSV or PDF.
Stored locally in your browser.
Date Sample Ca (mg/L) Mg (mg/L) TH (mg/L as CaCO3) Class Temp (°C)
No entries yet. Calculate, then click “Add to history”.

Example Data Table

Typical water samples (illustrative values) and the resulting hardness category.
Sample Ca (mg/L) Mg (mg/L) Total Hardness (mg/L as CaCO3) Category
Municipal Tap 35 8 120.7 Hard
Shallow Well 60 18 223.5 Very Hard
RO Permeate 3 1 11.6 Soft
Cooling Tower Makeup 45 14 170.7 Hard
Category bands (mg/L as CaCO3): Soft < 60, Moderately Hard 60–119, Hard 120–179, Very Hard ≥ 180.

Formula Used

Total hardness is commonly reported as mg/L as CaCO3. This calculator converts calcium and magnesium into equivalent CaCO3 hardness, then sums them:

  • Ca hardness (as CaCO3) = Ca (mg/L) × 2.497
  • Mg hardness (as CaCO3) = Mg (mg/L) × 4.118
  • Total hardness = Ca hardness + Mg hardness

Conversion factors come from 50 / equivalent weight for each ion (divalent Ca2+ and Mg2+). If you enter mmol/L or meq/L, the tool first converts to mg/L using atomic or equivalent weights.

How to Use This Calculator

  1. Enter calcium and magnesium using your lab’s units.
  2. Pick units for each ion (mg/L, mmol/L, or meq/L).
  3. Optional: add sample name and temperature for reporting.
  4. Click Calculate Total Hardness to see results below the header.
  5. Click Add to history to build an exportable sample log.
  6. Download CSV or PDF when your list is complete.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.