Anion gap calculator
Enter electrolyte results from a blood test to calculate the anion gap, which helps interpret metabolic acidosis.
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How to use it
- Enter sodium (na), chloride (cl), bicarbonate (hco3), potassium k (optional), albumin (optional) and albumin unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Anion gap = Na - (Cl + HCO3). With potassium: Na + K - (Cl + HCO3). Albumin-corrected = gap + 2.5 × (4.0 - albumin in g/dL).
Example
Inputs: Sodium (Na) = 140 mmol/L, Chloride (Cl) = 104 mmol/L, Bicarbonate (HCO3) = 24 mmol/L, Albumin unit = g/dL. Result: Anion gap: 12 mmol/L.
Limits and caveats
- The normal range differs between labs and analyzers, so compare with the range printed on your report.
- The albumin correction is an approximation of 2.5 per 1 g/dL.
- An educational estimate that does not replace assessment by a doctor or pharmacist.
Questions about this tool
What is the anion gap used for?
It helps sort the causes of metabolic acidosis; a high gap points to extra acids such as ketones or lactate.
Why correct for albumin?
Albumin is the largest unmeasured anion, so low albumin lowers the gap and can hide a high gap acidosis.
Should I enter potassium?
It is optional. Many labs calculate the gap without it, and adding it raises the result by the potassium value.