All calculatorsWater Hardness Calculator
Compute total hardness as mg/L as CaCO₃ (≈ ppm) from either ion concentrations (Ca²⁺, Mg²⁺) or from an EDTA titration. Get steps, a mini chart, a hardness gauge, and convenient unit conversions (gpg, °dH, °fH, meq/L, mmol/L).
Background
“Water hardness” primarily reflects dissolved Ca²⁺ and Mg²⁺. It is commonly reported as mg/L as CaCO₃. From ion concentrations: Hardness (as CaCO₃) = 2.497 × [Ca (mg/L)] + 4.118 × [Mg (mg/L)]. From an EDTA titration (1:1 with total hardness), use Hardness (mg/L as CaCO₃) = (MEDTA × VEDTA(L) × 50,000) / Vsample(mL).
How to use this calculator
- Choose method: Ion concentrations (Ca²⁺, Mg²⁺) or EDTA titration.
- We convert all units and report total hardness in mg/L as CaCO₃ (≈ ppm), plus gpg, °dH, °fH, meq/L, mmol/L.
- Toggle sig-fig rounding, show steps, a mini chart, and a hardness gauge.
Formula & Equation Used
From ions: Hardness (mg/L as CaCO₃) = 2.497·[Ca (mg/L)] + 4.118·[Mg (mg/L)]
From EDTA titration: Hardness (mg/L as CaCO₃) = (M_EDTA · V_EDTA(L) · 50,000) / V_sample(mL)
Common conversions: 1 gpg = 17.118 mg/L; 1 °dH = 17.848 mg/L; 1 °fH = 10 mg/L; meq/L = (mg/L as CaCO₃)/50; mmol/L (as CaCO₃) = (mg/L as CaCO₃)/100.
Example Problems & Step-by-Step Solutions
Example 1 — From ions
Ca = 40 mg/L, Mg = 12 mg/L → Hardness = 2.497×40 + 4.118×12 = ~158 mg/L as CaCO₃ (moderately hard).
Example 2 — From EDTA
M_EDTA=0.0100 M; V_EDTA=12.40 mL = 0.01240 L; V_sample=100.0 mL → Hardness = (0.0100×0.01240×50,000)/100.0 = 62.0 mg/L as CaCO₃ (soft).
Frequently Asked Questions
Q: What ranges define soft vs hard water?
A common scale (as CaCO₃, mg/L): 0–60 soft, 61–120 moderately hard, 121–180 hard, >180 very hard.
Q: Why convert to “as CaCO₃”?
It standardizes results across different ions (primarily Ca²⁺/Mg²⁺) using equivalent weight relative to CaCO₃.
Q: Does EDTA titration measure total hardness?
Yes, standard procedures (with buffer/indicator) capture combined Ca²⁺ + Mg²⁺ hardness.
