Chemistry

Osmolar Gap

Measured minus calculated osmolality.

Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.

When to use

Use when a toxic alcohol (methanol, ethylene glycol) ingestion is suspected; a raised gap suggests unmeasured osmotically active substances.

Why use

It flags unmeasured osmoles that routine tests would miss.

Critical actions

Calculated osmolality = 2×Na + glucose + urea (mmol/L). A normal gap does not fully exclude early toxic-alcohol ingestion. Discuss with toxicology if suspected.

Evidence & references

  1. Osmolar gap = measured − calculated osmolality; normal <10 mOsm/kg.

Related calculators

Calculated Serum OsmolalityEstimated osmolality from electrolytes.Anion GapSerum anion gap for metabolic acidosis.Delta Ratio (Acid–Base)Detects mixed metabolic acid–base disorders.

Need a calculator we don't have — or a custom tool?

We build evidence-led clinical calculators, dashboards and reference tools for teams.

Request a Custom Tool ☎ +44 7448 439750
☎ Call Get a Proposal