Serum Osmolarity Calculator

Calculates expected serum osmolarity, for comparison to measured osmolality to detect unmeasured compounds in the serum.

Serum Osmolality Calculator

Estimates serum osmolality and calculates the osmolal gap when a measured serum osmolality is available.

Formula: 2 × sodium + glucose + urea (+ ethanol).
The calculator automatically converts values entered in mg/dL.

Sodium *

Usually 136–145 mmol/L. Enter a valid sodium value.

Glucose *

Select the unit reported by the laboratory. Enter a valid glucose value.

Urea / BUN *

Use urea in mmol/L or BUN in mg/dL. Enter a valid urea or BUN value.

Serum Ethanol (optional)

Include only when a serum ethanol result is available.

Measured Serum Osmolality (optional)

Used to calculate the osmolal gap.

Calculated Serum Osmolality —

This calculator provides an estimate only. Interpret results with the clinical presentation, local laboratory method, and local clinical guidance.