mEq/L to mg/L Converter
Common Conversions
| mEq/L | mg/L |
|---|---|
| 0.1 | 0.1×AW/v |
| 0.5 | 0.5×AW/v |
| 1 | AW/v |
| 2 | 2×AW/v |
| 5 | 5×AW/v |
| 10 | 10×AW/v |
| 20 | 20×AW/v |
| 50 | 50×AW/v |
| 100 | 100×AW/v |
| 200 | 200×AW/v |
| 500 | 500×AW/v |
| 1000 | 1000×AW/v |
Why this conversion matters in chemistry
Electrolyte-replacement IV-fluid math brings this up often. A 140 mEq/L serum sodium reading from a basic metabolic panel corresponds to 3219 mg/L of Na — the form a USP <797> compounding-pharmacy bulk-admixture worksheet writes the same quantity in. The conversion uses mg/L = mEq/L × MW/valence; for Na (MW 22.99, valence 1), the factor is 23. The mEq notation is the natural one for clinical work because it directly reflects charge balance across the cell membrane and through the kidney; mass-based mg/L is the form pharmacy compounding documents and reagent prep ledgers expect.
Formula
Where the factor comes from
An equivalent is not a fixed amount of substance. It is whatever quantity supplies one mole of charge, so its size depends on which ion is under discussion and, in redox work, on which reaction was chosen. Divide the atomic or formula weight by the charge number and the equivalent weight falls out: 22.99 for Na⁺, 20.04 for Ca²⁺, 48.03 for SO₄²⁻. Multiply mEq/L by that and the milli prefixes cancel, leaving mg/L. Neither half of the factor is exact. Standard atomic weights are measured, several published as intervals because isotopic abundance varies by source, and the charge number is a modeling decision rather than a measurement for species whose speciation shifts with pH. IUPAC has deprecated the equivalent; clinical and water-treatment practice has not.
Precision and significant figures
Equivalent weights for the common ions are known far better than any sample they get applied to. Sodium's 22.990 offers five figures and chloride's 35.45 four, while the analyzer producing the mEq/L reading delivers two or three. Ion-selective electrodes and ion chromatography at these levels carry method uncertainty of a few percent once calibration, dilution and matrix effects are counted in, so a result printed as 3218.6 mg/L from a 140 mEq/L input is arithmetic dressed up as data. Report 3220 mg/L, or 3.22 g/L. The genuinely fussy input is the charge number: exact when right, and wrong by a clean factor of two or three when not — never by a few percent.
Worked Examples
Sodium — the most common monovalent cation in clinical electrolyte panels.
Calcium — divalent, so the mEq and mg scales differ by half the atomic weight.
Potassium — the second monovalent cation that dominates clinical electrolyte work.
Chloride — the principal monovalent anion in extracellular fluid.
Common mistakes
Charge number confused with atom count
Bicarbonate carries one unit of charge despite having five atoms, and sulfate carries two despite having five as well. The divisor is the ion's charge, not its size or its complexity. Polyatomic ions are where this goes wrong most often, because the formula looks complicated enough that a larger divisor feels right.
Applied to species that carry no charge
Glucose, urea and creatinine are neutral molecules, so no equivalent weight exists for them and mEq/L describes nothing. A worksheet that runs a generic weight-over-valence formula down every row will still produce numbers for those analytes, formatted identically to the ones that mean something. Charge-based units belong to ions only.
Salt formula weight used for the ion
Potassium delivered as KCl still has an equivalent weight of 39.10, not the salt's 74.55. The chloride rides along and is separately reportable, but it is not part of the potassium result. Sodium from NaCl, calcium from CaCl₂ and magnesium from MgSO₄ all invite the same substitution, and each inflates the answer by the mass of the counter-ion.