Osmolal Gap Calculator
Estimate osmolal gap from measured and calculated serum osmolality.
Understanding this tool
Why nurses use it
Osmolal gap (measured minus calculated osmolality) suggests unmeasured osmoles — toxic alcohols, ethanol, or other substances in ingestion workups.
When to use it
Use when toxic ingestion, unexplained osmolality, or high-gap metabolic acidosis is suspected.
Calculate
How to use this calculator
- Enter measured osmolality and lab sodium, glucose, BUN.
- Review gap — elevated gap warrants further toxicology workup.
How the calculation works
Calculated osm ≈ 2×Na + glucose/18 + BUN/2.8 (US units). Gap = measured − calculated.
Formula used by this tool — verify units before applying at the bedside.
Worked example
Limitations & clinical notes
- Calculated osm formula variants exist; use local lab alignment.
- Ethanol requires separate calculation if suspected.
References
Key sources: Toxic alcohol ingestion workups.
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Disclaimer: This calculator is for educational and bedside double-check purposes only. It does not replace institutional protocols, prescriber orders, pharmacist verification, or clinical judgment. Always follow your local policies — especially for high-risk medications, infusions, pediatrics, and critical care. If the patient is acutely unwell, escalate immediately rather than relying on any calculator output.