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Osmolar Gap Calculator

Osmolar gap = measured − calculated osmolality.

Compute the osmolar gap between measured serum osmolality and the calculated osmolality from sodium, glucose and BUN. A gap > 10 mOsm/kg suggests an unmeasured osmole such as ethanol, methanol or ethylene glycol.

Priya Venkatesan By Priya Venkatesan
Published Last reviewed 1 min read

Inputs

mEq/L
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 osmolality = 2·Na + glucose/18 + BUN/2.8. Gap = measured − calc.

In depth

Compute the osmolar gap between measured serum osmolality and the calculated osmolality from sodium, glucose and BUN. A gap > 10 mOsm/kg suggests an unmeasured osmole such as ethanol, methanol or ethylene glycol.