mg ↔ mEq Converter
Convert milligrams to milliequivalents (and back) for potassium, sodium, calcium, magnesium and more.
Potassium (K⁺)
- mg600 mg
- mEq15.345 mEq
- mmol15.345 mmol
1 mEq K = 39.1 mg
Frequently asked questions
mEq (milliequivalent) accounts for the ion's electrical charge (valence). 1 mmol of a +1 ion (K, Na) provides 1 mEq, but 1 mmol of a +2 ion (Ca, Mg) provides 2 mEq because each ion carries twice the charge. So 39 mg of potassium = 1 mEq, but 40 mg of calcium ≠ 2 mEq (it's only 2 mEq because Ca is divalent — so it's actually 2 mEq).
KCl has molecular weight 74.5. 600 mg ÷ 74.5 = 8.05 mmol KCl = 8.05 mmol K (since KCl is 1:1). Each mmol K = 1 mEq (valence 1), so 600 mg KCl ≈ 8 mEq K. The tool handles this for you: pick KCl as the ion, enter 600 mg.
mmol is the SI unit (used in Europe, lab reports). mEq is the older clinical unit (used in US, drug labels, prescribing). Conversion: mEq = mmol × valence. So 5 mmol of K = 5 mEq (valence 1); 5 mmol of Ca = 10 mEq (valence 2).
Historical convention. US clinical pharmacology adopted mEq because it lets you compare ions on a charge-equivalence basis without thinking about valence. For example, you can directly compare 'serum K+ 4.5 mEq/L' against 'IV NaCl 154 mEq/L' regardless of valence. SI units (mmol) are theoretically cleaner but require the valence step for comparison.
On a prescription, the strength can refer to the salt (e.g. 600 mg KCl) or the elemental ion (e.g. 8 mEq K+). Labels in the US sometimes give both. The tool's salt entries (KCl, NaCl, CaCO3, MgSO4) handle salt-to-ion conversion directly. Pick the ion entry (K, Na, Ca, Mg) when the label is already in elemental form.
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