What is a milliequivalent (mEq)?

A milliequivalent is 1/1000 of an equivalent — the amount of an ion that can react with or replace one mole of hydrogen ions. For monovalent ions (Na+, K+, Cl-), 1 mmol = 1 mEq. For divalent ions (Ca2+, Mg2+), 1 mmol = 2 mEq.

How do I convert mg to mEq?

mEq = (mg ÷ molecular weight) × valence. For example, 23 mg of sodium (MW 23, valence 1) = (23 ÷ 23) × 1 = 1 mEq. For calcium (MW 40, valence 2): 20 mg = (20 ÷ 40) × 2 = 1 mEq.

What is the difference between mmol and mEq?

mmol (millimole) measures the amount of substance by particle count; mEq also accounts for ionic charge. For monovalent ions (valence = 1), mEq = mmol. For divalent ions (valence = 2), mEq = 2 × mmol.

What is a milliosmole (mOsm)?

A milliosmole measures the osmotic activity of particles in solution. For ions that do not associate (ideal dilute solution), 1 mmol of a monovalent electrolyte contributes 1 mOsm. This calculator uses the ideal (non-dissociating) approximation.

Why does phosphate have two options?

Phosphate exists in different ionization states at physiological pH. Monobasic phosphate (H2PO4-) has valence 1; dibasic phosphate (HPO4 2-) has valence 2. The mix at pH 7.4 is roughly 80% dibasic. This calculator provides both forms so you can match your clinical context.

Milliequivalent Calculator

Name: Milliequivalent Calculator
Availability: InStock
Author: Nham Vu

Convert between milliequivalents (mEq), millimoles (mmol), milligrams (mg), and milliosmoles (mOsm) for common electrolytes and ions used in clinical and IV calculations.

Input

Electrolyte / Ion

Input unit

Amount

Results

mEq

—

mmol

—

mOsm

—

Quick Reference — Common Electrolytes (per 1 mEq)

Ion	MW (g/mol)	Valence	mg per 1 mEq	mmol per 1 mEq

Copied!

Summary

Convert between milliequivalents (mEq), millimoles (mmol), milligrams (mg), and milliosmoles (mOsm) for common electrolytes and ions used in clinical and IV calculations.

How it works

Select the electrolyte or ion from the dropdown.
Choose the input unit: mEq, mmol, mg, or mOsm.
Enter the numeric amount.
The calculator shows all four equivalent values in real time.
Use the copy button next to any result to copy that value to the clipboard.

Use cases

Verify IV electrolyte orders before compounding.
Convert lab values reported in mg/dL to mEq/L for clinical interpretation.
Calculate osmolar contributions of individual electrolytes to a solution.
Double-check unit conversions when transitioning between US and SI reporting.
Pharmacy students learning electrolyte unit relationships.
Cross-check mEq-to-mmol conversions for monovalent vs. divalent ions.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu