mEq ↔ mg Conversion

Formula

mg  =  mEq  ×  (molecular weight ÷ valence)
mEq =  mg   ×  (valence ÷ molecular weight)

An equivalent (Eq) is one mole of charge. Monovalent ions (K⁺, Na⁺) have valence 1, 1 mEq = 1 mmol. Divalent ions (Ca²⁺, Mg²⁺) have valence 2, 1 mEq = 0.5 mmol.

Quick reference (the values you'll see most)

• KCl: 1 mEq K = 74.55 mg KCl. So 20 mEq = ~1,491 mg = 1.5 g KCl.
• NaCl: 1 mEq Na = 58.44 mg NaCl. 0.9% saline contains 154 mEq Na/L.
• NaHCO₃: 1 mEq = 84 mg. 1 amp (50 mL of 8.4%) = 50 mEq = 4.2 g.
• MgSO₄·7H₂O: 1 g = 8.12 mEq Mg. 2 g = 16.24 mEq Mg (typical OB pre-eclampsia bolus).
• Calcium gluconate 10%: 1 g/10 mL = 4.65 mEq Ca²⁺. 1 amp = ~4.5 mEq.

Why this matters

Drug labeling has standardized on mg for most medications, but cardiology and renal protocols still write electrolyte orders in mEq because that reflects the physiologically meaningful unit (charge). Confusing the two has been the root cause of multiple reported potassium overdoses; double-check every electrolyte order both ways before administration.