Serum Osmolality Calculator

Find serum osmolality.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

This calculator estimates serum osmolality from sodium, glucose, and blood urea nitrogen (BUN) using the standard formula: 2×Na + glucose/18 + BUN/2.8 (values in mg/dL). It reflects the concentration of dissolved particles in the blood and helps identify whether a measured osmolality gap is present.

Clinicians, lab technicians, and medical students use it alongside a directly measured osmolality to screen for unmeasured osmotically active substances such as toxic alcohols. Enter sodium, glucose, and BUN to get the calculated osmolality in mOsm/kg.

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