Convert mmol ↔ mEq
Use this calculator to quickly convert between millimoles (mmol) and milliequivalents (mEq) using ion valence (charge).
What is the difference between mmol and mEq?
Both mmol and mEq are used in chemistry, medicine, and lab reporting, but they describe slightly different ideas:
- mmol (millimole) tells you how many particles are present (amount of substance).
- mEq (milliequivalent) tells you the chemical combining power, which depends on electric charge (valence).
For ions, valence matters. A divalent ion (charge 2) contributes twice as many equivalents per mole compared with a monovalent ion (charge 1).
mEq = mmol × |valence|
mmol = mEq ÷ |valence|
How to use this mmol mEq calculator
Step-by-step
- Select conversion direction: mmol to mEq or mEq to mmol.
- Enter the amount you know.
- Choose a common ion preset or manually type the valence.
- Click Calculate to see the converted value instantly.
The calculator always uses the absolute valence (|z|), so both +2 and -2 are treated as valence 2 for conversion.
Common ion valences (quick reference)
| Ion | Symbol | Valence |z| | Relationship |
|---|---|---|---|
| Sodium | Na⁺ | 1 | 1 mmol = 1 mEq |
| Potassium | K⁺ | 1 | 1 mmol = 1 mEq |
| Chloride | Cl⁻ | 1 | 1 mmol = 1 mEq |
| Calcium | Ca²⁺ | 2 | 1 mmol = 2 mEq |
| Magnesium | Mg²⁺ | 2 | 1 mmol = 2 mEq |
| Phosphate | PO₄³⁻ | 3 | 1 mmol = 3 mEq |
Worked examples
Example 1: Convert 8 mmol calcium to mEq
Calcium is divalent, so valence = 2.
mEq = 8 × 2 = 16 mEq
Example 2: Convert 30 mEq potassium to mmol
Potassium is monovalent, so valence = 1.
mmol = 30 ÷ 1 = 30 mmol
Example 3: Convert 18 mEq magnesium to mmol
Magnesium valence = 2.
mmol = 18 ÷ 2 = 9 mmol
Why this conversion matters
In clinical and lab contexts, many electrolyte values are interpreted by charge activity, not just particle count. Using mEq helps compare ions on an equivalent-charge basis. That is especially helpful when adjusting solutions, interpreting electrolyte replacement, or reviewing lab chemistry data.
Common mistakes to avoid
- Forgetting valence: mmol and mEq are only identical when valence is 1.
- Using signed charge: for conversion, use the absolute value of charge (|z|).
- Mixing units: double-check whether your source value is mmol or mEq before converting.
- Rounding too early: carry extra decimals during calculations and round at the end.
FAQ
Is 1 mmol always equal to 1 mEq?
No. Only for monovalent ions (valence 1). For valence 2 ions, 1 mmol = 2 mEq.
Can this calculator be used for anions and cations?
Yes. The conversion uses absolute charge, so both positive and negative ions work the same way.
Does this replace medical advice?
No. This is an educational conversion tool. Clinical decisions should follow professional protocols and verified lab context.