Osmolar & Anion Gap Calculator

Osmolar Gap & Anion Gap Calculator

For ABG/Metabolic Emergencies, Toxic Alcohols, and High/Normal AG Metabolic Acidosis.

Na⁺

Cl⁻

HCO₃⁻ (Total CO₂)

Albumin (g/dL)

Glucose

BUN / Urea

Ethanol

Measured Osmolality (mOsm/kg)

Temp (°C) (optional)

Notes

Units

Calculated Osmolality = 2×Na + Glucose/18 + BUN/2.8 + Ethanol/3.7 (US)
In SI (mmol/L): 2×Na + Glucose + Urea + Ethanol
Osmolar Gap = Measured Osm − Calculated Osm
Anion Gap (AG) = Na − (Cl + HCO₃)
Albumin-corrected AG = AG + 2.5 × (4 − Albumin[g/dL])
Red flags for toxic alcohols: Osm Gap ≥ 10–20 mOsm/kg and/or High AG metabolic acidosis.