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Serum Osmolality Calculator

Calculated serum osmolality and osmolar gap.

Compute calculated serum osmolality from sodium, glucose, BUN, and (optionally) ethanol levels using the standard 2·Na + glucose/18 + BUN/2.8 + ETOH/3.7 formula. Reports the osmolar gap if measured osmolality is provided.

Priya Venkatesan By Priya Venkatesan
Published Last reviewed 1 min read

Inputs

mmol/L
mg/dL
mg/dL
mg/dL
mOsm/kg

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Calc Osm = 2·Na + glucose/18 + BUN/2.8 + ethanol/3.7. Gap = measured − calculated.

In depth

Compute calculated serum osmolality from sodium, glucose, BUN, and (optionally) ethanol levels using the standard 2·Na + glucose/18 + BUN/2.8 + ETOH/3.7 formula. Reports the osmolar gap if measured osmolality is provided.