This page explains how to convert milliequivalents per liter (mEq/L) to millimoles per liter (mmol/L) for common clinical ions. For monovalent ions like sodium (Na⁺) or potassium (K⁺), the numeric values in mEq/L and mmol/L are the same. For divalent ions such as calcium (Ca²⁺) or magnesium (Mg²⁺), you divide the mEq/L value by 2 to obtain mmol/L.
mEq/L to mmol/L Formula
mEq/L is a concentration measure that incorporates both the amount of substance and its electrical charge. mmol/L is a more purely chemical measure that reflects the number of particles regardless of charge. The two are linked through the ion’s valence (absolute charge, |z|) using:
- mEq/L = mmol/L × |z|
- mmol/L = mEq/L ÷ |z|
Here, |z| is the absolute value of the ion’s charge. Some common examples:
- Na⁺, K⁺, Cl⁻, HCO₃⁻: |z| = 1
- Ca²⁺, Mg²⁺: |z| = 2
- PO₄³⁻: |z| = 3
Once you know the charge, the conversion is straightforward. For example, 10 mEq/L of Ca²⁺ corresponds to 10 ÷ 2 = 5 mmol/L, while 10 mEq/L of Na⁺ corresponds to 10 ÷ 1 = 10 mmol/L.
mEq/L to mmol/L conversion table
The table below shows example conversions for a 10 mEq/L concentration of several common ions using the relationship mmol/L = mEq/L ÷ |z|.
| Ion | Typical |z| | 10 mEq/L in mmol/L |
|---|---|---|
| Sodium (Na⁺) | 1 | 10 mmol/L |
| Potassium (K⁺) | 1 | 10 mmol/L |
| Chloride (Cl⁻) | 1 | 10 mmol/L |
| Bicarbonate (HCO₃⁻) | 1 | 10 mmol/L |
| Calcium (Ca²⁺) | 2 | 5 mmol/L |
| Magnesium (Mg²⁺) | 2 | 5 mmol/L |
| Phosphate (PO₄³⁻) | 3 | 3.33 mmol/L |
In practice, the lab often reports either mmol/L or mEq/L depending on the analyte and local conventions. Understanding the role of the ion’s charge makes it easy to move between the two and compare results across different references or calculators.
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