Serum Osmolality Calculator

This calculator works out serum osmolality from the sodium, glucose and urea on a laboratory report, in conventional or SI units. Enter those values, add ethanol if it was measured, and it returns the calculated osmolality with each component shown separately. Supply the osmometer's measured result as well and it also reports the osmolal gap. Formulas and reference ranges differ between laboratories, and interpreting either figure belongs to the team treating the patient.

Calculator Type

Sodium in mEq/L, glucose and blood urea nitrogen in mg/dL, straight off the report.

BUN, not urea. A urea result in mg/dL is about 2.14 times the BUN.
Leave at zero unless ethanol was measured. It is added as mg/dL divided by 3.7.
The osmometer result. Fill this in to get the osmolal gap; leave it at zero for the calculated value alone.
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Sodium, glucose and urea all in mmol/L, which is how most laboratories outside the United States report them.

Urea in mmol/L, not BUN in mg/dL. Note the unit on the report before typing.
Leave at zero unless ethanol was measured. In mmol/L it is added straight on.
The osmometer result. Fill this in to get the osmolal gap; leave it at zero for the calculated value alone.
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