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Serum Osmol Gap Calculator

Difference between measured and calculated osmolality.

Osmol gap = measured osmolality − calculated osmolality. A gap > 10 mOsm/kg suggests unmeasured osmoles such as ethanol, methanol, or ethylene glycol.

Priya Venkatesan By Priya Venkatesan
Published Last reviewed 1 min read

Inputs

mOsm/kg
mEq/L
mg/dL
mg/dL

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

Gap = measured − (2·Na + Glu/18 + BUN/2.8)

In depth

Osmol gap = measured osmolality − calculated osmolality. A gap > 10 mOsm/kg suggests unmeasured osmoles such as ethanol, methanol, or ethylene glycol.