mmol/L to Milliequivalents/L Converter
Common Conversions
| mmol/L | mEq/L |
|---|---|
| 0.1 | 0.1×v |
| 0.5 | 0.5×v |
| 1 | 1×v |
| 2 | 2×v |
| 5 | 5×v |
| 10 | 10×v |
| 20 | 20×v |
| 50 | 50×v |
| 100 | 100×v |
| 140 | 140×v |
| 200 | 200×v |
| 500 | 500×v |
Why this conversion matters in chemistry
Critical-care calcium replacement is a typical place to need it. A 2.5 mmol/L serum calcium reading on an SI-aligned clinical-chemistry report is 5 mEq/L on a USP <797> compounding worksheet — the divalent Ca²⁺ scales by 2 between mole-based and charge-based notations. Origin of the 1 mEq per mmol per unit valence: the equivalent definition: one equivalent supplies one mole of charges. Mostly bookkeeping at the boundary of SI clinical reporting and traditional bedside electrolyte management documentation.
Formula
Where the factor comes from
An equivalent is not a property of a substance; it is a property of a substance in a stated reaction. The definition is one mole of charge, so the multiplier is however many units of charge one mole of the species carries — and that has to be decided before any arithmetic happens. For a simple ion the decision is easy: the charge number, 1 for Na⁺ and Cl⁻, 2 for Ca²⁺ and Mg²⁺. For an acid undergoing neutralization the count is transferable protons, which gives sulfuric acid two equivalents per mole. For a redox couple it is electrons, which gives permanganate five per mole in acid. Every one of those multipliers is an exact integer, so nothing measured enters the conversion. Deciding which integer applies is the whole of the work; the multiplication is trivial.
Precision and significant figures
Multiplying by a small integer neither adds nor removes significant figures. A monovalent ion at 4.2 mmol/L is 4.2 mEq/L, and a divalent one at 1.35 mmol/L is 2.70 mEq/L — that trailing zero is real, since doubling an exact figure preserves it rather than inventing anything. What the arithmetic cannot do is make the label unambiguous. For monovalent species the two columns print identical digits, so a number stripped of its unit is unrecoverable: 140 could be either, and nothing in the value says which. Potentiometric electrolyte analyzers typically resolve to about a tenth of a millimole per liter, and the abundant ions are often reported as whole numbers, so two or three figures is the honest ceiling however many the multiplier appears to justify.
Worked Examples
Normal serum sodium — monovalent, identical values.
Normal serum calcium — divalent, mEq is double the mmol.
Normal potassium — monovalent identity.
Normal magnesium — divalent, mEq is double.
Common mistakes
Equivalents of an acid count protons
Sulfuric acid at 1 mmol/L is 2 mEq/L because each molecule delivers two protons, not because sulfate carries a charge of two — the two answers happen to agree here. Phosphoric acid breaks the coincidence: it supplies one, two or three protons depending on the endpoint chosen, so its multiplier belongs to the titration rather than to the bottle.
Charge sign carried into the multiplier
The multiplier is the magnitude of the charge number. Chloride at 1 mmol/L is 1 mEq/L, not −1, and a spreadsheet pulling a signed charge from a lookup column will hand back negative equivalents for every anion in the sheet. Signs matter when cation and anion totals are compared, but they belong to that comparison, not to the conversion feeding it.
A dissolved salt has no single valence
One millimole per liter of CaCl₂ is not simply 2 mEq/L. It supplies 1 mmol/L of Ca²⁺, worth 2 mEq/L, and 2 mmol/L of Cl⁻, worth another 2 mEq/L. Equivalents attach to ions, so a salt has to be broken into the ions it releases and the multiplier applied to each of them separately.