Calculated osmolality and the gap from a measured value — sodium in mEq/L, others in mg/dL
Sodium (mEq/L)
Glucose (mg/dL)
BUN (mg/dL)
Ethanol (mg/dL) — optional
Measured osmolality (mOsm/kg) — optional
Enter sodium, glucose, and BUN to calculate
Evidence
Original publication
Smithline N, Gardner KD Jr. Gaps — anionic and osmolal. Described the osmolal gap (measured minus calculated osmolality) as a screen for unmeasured low-molecular-weight solutes such as methanol, ethylene glycol, and ethanol.
JAMA, 1976
Open source
Validation
Purssell RA, Pudek M, Brubacher J, Abu-Laban RB. Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap. Confirmed the ethanol/3.7 term and that a normal osmolal gap is roughly −10 to +10 mOsm/kg, with wide inter-individual variation limiting its sensitivity for toxic alcohols at low concentrations.
Annals of Emergency Medicine, 2001
Open source
Last reviewed: 2026-09
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