Serum Osmolality/Osmolarity Calculator

Serum Osmolar Gap

Calculates expected serum osmolarity to detect unmeasured compounds (toxic alcohols, etc.) by comparing to measured osmolality.

Sodium

Norm: 136 – 145

mEq/L

BUN

Norm: 8 – 20

mg/dL

Glucose

Norm: 70 – 105

mg/dL

Serum alcohol concentration

Optional; for accurate estimation

mg/dL

Measured serum osm

Normal value is 285 mmol/kg

mOsm/kg

mOsm/kg
Osmolar Gap

Normal

Calculated: 0 mOsm/L

*Using Purssell et al. equation

Toxic Alcohols: Gap >10 suggests unmeasured osmoles (Methanol, Ethylene Glycol).

Isopropyl Alcohol: Causes a large osmolar gap but no anion gap acidosis.

Serum Osmolarity and Osmolar Gap Calculator