mg/l to mmol/l Converter

By: Patrick Myers Patrick Myers is the CEO and Founder of Calculator Academy. He has over eight years of experience developing online calculators and holds a B.S. in Mechanical Engineering. His work focuses on formula implementation, calculator accuracy, unit conversions, and creating practical tools that are easy to use.

Last Updated: October 20, 2026

Convert mg/L or mg/dL using the solute’s molar mass.

Use the reported chemical species and mass basis. This tool converts units; it does not interpret laboratory results.

Presets are rounded. Editing this value selects Custom.

This page shows how to turn a concentration reported in milligrams per liter (mg/L) into millimoles per liter (mmol/L). mg/L is a mass-based unit, whereas mmol/L measures the amount of the specified chemical entity per liter. To move between them you need the substance’s molar mass in g/mol.

Unit definitions and chemical basis: IUPAC amount concentration, CIAAW atomic weights, and PubChem entries for lactate and lactic acid.

mg/L to mmol/L Formula

For a given substance with molar mass M in g/mol, the connection between mg/L and mmol/L is:

  • mg/L = mmol/L × M
  • mmol/L = mg/L ÷ M

Here, M is the molar mass of the specified chemical entity in grams per mole. These are rounded conventional values, not exact constants:

  • Sodium (Na⁺): M ≈ 22.99 g/mol
  • Potassium (K⁺): M ≈ 39.10 g/mol
  • Calcium (Ca²⁺): M ≈ 40.08 g/mol
  • Magnesium (Mg²⁺): M ≈ 24.31 g/mol
  • Chloride (Cl⁻): M ≈ 35.45 g/mol
  • Glucose: M ≈ 180.16 g/mol
  • Urea: M ≈ 60.06 g/mol

Once the molar mass is known, the arithmetic is simple. For example, 90 mg/L of sodium corresponds to 90 ÷ 22.99 ≈ 3.91 mmol/L. Likewise, 40 mg/L of calcium is roughly 40 ÷ 40.08 ≈ 1.00 mmol/L, and 540 mg/L of glucose is about 540 ÷ 180.16 ≈ 3.00 mmol/L.

mg/L to mmol/L conversion table

The table below lists example conversions for a 100 mg/L concentration using mmol/L = mg/L ÷ M.

Substance Molar mass (g/mol) 100 mg/L in mmol/L
Sodium (Na⁺) 22.99 4.35 mmol/L
Potassium (K⁺) 39.10 2.56 mmol/L
Chloride (Cl⁻) 35.45 2.82 mmol/L
Calcium (Ca²⁺) 40.08 2.50 mmol/L
Magnesium (Mg²⁺) 24.31 4.11 mmol/L
Glucose 180.16 0.56 mmol/L
Urea 60.06 1.67 mmol/L

In practice, some laboratories report results in mg/L while others use mmol/L. Convert only when the same analyte and reporting basis are used: phosphate as PO₄ differs from phosphorus, urea differs from urea nitrogen, and lactate ion differs from lactic-acid equivalent. Preset masses are rounded, and triglyceride mixtures have no single molar mass; the calculator’s875 g/mol row is an explicitly assumed mean, not a universal clinical factor. Unit conversion does not interpret a result or replace the laboratory’s own reference interval.

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mg/l to mmol/l Converter screenshot