mEq vs mmol: The Quick Conversion Guide Every Healthcare Pro Needs
mEq measures the electrical charge of an ion; mmol measures the number of ion particles. 1 mmol of a monovalent ion equals 1 mEq, while 1 mmol of a divalent ion equals 2 mEq.
On the floor, sodium is dosed in mEq because charge balance is critical for cardiac rhythms; calcium, magnesium, and phosphate labs come back in mmol, so nurses scramble to reconcile the two. A simple “× valence” rule saves time and prevents infusion errors.
Key Differences
mEq = mmol × valence. Monovalent (Na+, K+) keeps numbers equal; divalent (Ca2+, Mg2+) doubles mEq. Sodium 154 mmol/L saline is 154 mEq/L; calcium gluconate 1 mmol gives 2 mEq.
Which One Should You Choose?
Use mEq for electrolyte replacement orders, TPN calculations, and dialysis baths. Use mmol when reading lab reports, pharmacopoeia monographs, or international guidelines. Always convert before mixing or titrating.
Examples and Daily Life
Patient gets 20 mmol KCl IV. That’s 20 mEq K+. If it were 20 mmol MgSO4, you’d infuse 40 mEq Mg2+. Quick mental math: multiply by ion charge.
Can I always divide mEq by 2 to get mmol?
Only if the ion is divalent. For monovalent ions, mEq and mmol are identical.
Why do some labs report phosphate in mmol while others use mg/dL?
mmol reflects particle count and follows SI units; mg/dL reflects mass and is legacy US practice. Convert with molecular weight: 1 mmol phosphate ≈ 31 mg.