Milliequivalents (mEq) Calculator
Convert a mass in milligrams to milliequivalents using the molar mass and valence — the unit used for electrolytes in clinical and lab work.
How it works
mEq = mass (mg) × valence ÷ molar mass (g/mol) · Equivalent weight = molar mass ÷ valence
An equivalent measures reactive or charge-carrying capacity rather than plain mass, which is why electrolytes are dosed in milliequivalents. One equivalent is one mole of charge, so dividing the molar mass by the ion’s valence gives the equivalent weight — the grams that carry one equivalent of charge. Milligrams divided by that equivalent weight, times 1000, gives milliequivalents; the tidy form is mass in mg times valence divided by molar mass.
Worked example
For 1000 mg (1 g) of NaCl (molar mass 58.44 g/mol, Na⁺ valence 1): mEq = 1000 × 1 ÷ 58.44 = 17.11 mEq. So 1 g of sodium chloride supplies about 17 mEq of sodium.
Sources: Equivalent (chemistry) — Wikipedia
Frequently asked questions
What is a milliequivalent?
A milliequivalent is one thousandth of an equivalent — one thousandth of a mole of charge. It lets you compare ions on the basis of the charge they carry rather than their raw mass, which matters for electrolyte balance.
How is mEq related to millimoles?
mEq = mmol × valence. For a singly charged ion like Na⁺ they are numerically equal, but for Ca²⁺ each millimole is 2 mEq and for PO₄³⁻ each millimole is 3 mEq.
What valence do I use for a salt?
Use the charge of the ion you are counting. For a compound, base the valence on the total charge of the cations (or anions) — for example CaCl₂ delivers 2 mEq of charge per millimole.
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This calculator is for educational purposes. Double-check important results before acting on them.