Osmolarity Calculator
Calculate serum osmolarity from sodium, glucose, and BUN using the standard clinical formula.
How to Use the Osmolarity Calculator
- Enter the serum sodium (Na⁺) in mEq/L.
- Enter the serum glucose in mg/dL.
- Enter the blood urea nitrogen (BUN) in mg/dL.
- Click Calculate to see osmolarity and interpretation.
Casi d'Uso
- •Evaluating hyponatremia and hypernatremia in clinical settings.
- •Assessing hydration status in ICU patients.
- •Teaching fluid and electrolyte physiology.
Formula
Formula: Osmolarity (mOsm/kg) = 2 × Na⁺ + glucose (mg/dL) / 18 + BUN (mg/dL) / 2.8.
Domande Frequenti
What is normal serum osmolarity?
Normal serum osmolarity is 280–295 mOsm/kg. Values below 280 indicate hypoosmolarity (dilution), while values above 295 indicate hyperosmolarity (dehydration or solute excess).
What does sodium contribute the most?
Sodium and its accompanying anions (mainly chloride and bicarbonate) account for about 90% of extracellular osmolarity. That's why the formula multiplies Na by 2.
Disclaimer
For educational purposes only. Not a substitute for clinical assessment. Serum osmolarity should be interpreted alongside clinical history, other labs, and measured osmolality when osmolar gap is suspected.