Chemistry
Water Hardness Calculator
Convert measured calcium and magnesium levels into total hardness expressed as calcium carbonate.
Your inputs
Change any value to update the result instantly.
Total hardness
298.59 mg/L as CaCO₃
Classification
Very hard water
Hardness in grains per gallon
17.443 gpg
Contribution from calcium
199.76 mg/L
Contribution from magnesium
98.83 mg/L
The factors 2.497 and 4.118 are the ratios of the CaCO₃ molar mass to the calcium and magnesium molar masses. Classification bands follow the USGS scale.
What this calculator does
Converts measured calcium and magnesium levels into total hardness expressed as calcium carbonate.
What your result means
Total hardness in mg/L as CaCO3, with the USGS classification band from soft to very hard.
Formula and working
Hardness (mg/L as CaCO₃) = 2.497 × [Ca²⁺] + 4.118 × [Mg²⁺]
- 1
Collect the inputs
Calcium concentration (Ca²⁺) = 80 mg/L; Magnesium concentration (Mg²⁺) = 24 mg/L
- 2
Apply the formula
Hardness (mg/L as CaCO₃) = 2.497 × [Ca²⁺] + 4.118 × [Mg²⁺]
- 3
Result
Total hardness = 298.59 mg/L as CaCO₃
Frequently asked questions
Symbols and assumptions
- [Ca2+]
- Calcium concentration in mg/L
- [Mg2+]
- Magnesium concentration in mg/L
- • Calcium and magnesium are the only significant hardness ions.
- • Factors 2.497 and 4.118 are the CaCO3 molar-mass ratios.
Sources and review
Reviewed 2026-09-22 · Next review 2027-09-22
- • Iron, manganese and strontium also add hardness but are not included. 1 grain per gallon equals 17.118 mg/L.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Report a mistake or request an improvement
Tell us if a formula, unit, explanation, or result needs attention. Your message will include this calculator’s name and page.
Related calculators
Activity Coefficient Calculator
Estimate the activity coefficient of an ion in a dilute solution using the Debye-Hückel limiting law.
Alligation Calculator
Work out how much of a weak and a strong solution to mix to reach a target strength.
Bleach Dilution Calculator
Find how much concentrated bleach and water to combine for a target available-chlorine strength.
Buffer Capacity Calculator
Measure how much strong acid or base a buffer absorbs for each unit of pH change.
Dilution Factor Calculator
Work out the dilution factor between a stock solution and the diluted solution you prepare.
Mass Percent Calculator
Find what share of a mixture's mass comes from one component.