Health

Serum Osmolality Calculator

Calculate osmolality with optional ethanol and osmolal gap.

Na (mEq/L)

Glucose (mg/dL)

BUN (mg/dL)

Ethanol (mg/dL)

Measured Osmolality (mOsm/kg)

Osmolality

Calc Osm = 2×Na + Glucose/18 + BUN/2.8 + EtOH/4.6. Normal 275–295. Gap = Measured − Calculated. Normal gap ≤10. Elevated gap suggests toxic alcohols (methanol, ethylene glycol).