Milliequivalent and millimole converter

Milliequivalents equal millimoles multiplied by the valence of the ion, and millimoles equal milligrams divided by molecular weight. Valence is what catches people: a divalent ion such as calcium gives twice the milliequivalents of a monovalent ion at the same molar amount.

When to use the meq and mmol calculator

Use whenever electrolytes are ordered in milliequivalents but supplied in milligrams, which is routine for potassium, calcium, magnesium and sodium salts.

The meq and mmol formula

mmol = mg ÷ molecular weight. mEq = mmol × valence. Reversing it, mg = (mEq × molecular weight) ÷ valence.

Worked example

Potassium chloride 1500 mg, molecular weight 74.5, valence 1. mmol = 1500 ÷ 74.5 = 20.1 mmol, and because valence is 1, that is also 20.1 mEq.

The mistake that costs marks

Valence is where this goes wrong. Potassium is monovalent so mEq and mmol are numerically equal, but calcium is divalent so 1 mmol is 2 mEq. Use the molecular weight of the whole salt, not the element, unless the question specifies elemental content.

Study aid, not a clinical tool

This calculator exists so you can learn the method and check your working for an examination. It is not medical advice and not clinical decision support, and it must not be used to make a decision about a real patient. Verify any result against your local formulary, the product literature and a qualified pharmacist. Our medical disclaimer sets out the full position.

Calculators you will usually need alongside this

Most questions that reach for one of these reach for another a step later, so these are the three that most often pair with it.

• Osmolarity calculator — Osmolarity
• Ratio strength and percentage converter — Ratio strength
• Dilution calculator (C1V1 = C2V2) — Dilution

Keep going

Calculations are only half of what examinations test. The other half is knowing why a drug does what it does, which is what decides whether a number you calculated is even the right number to be calculating. Start with Best pharmacy calculators. The drug class pages cover the mechanism behind the number, or browse the rest of the free calculators and try the practice questions.