Urea Nitrogen (BUN) Unit Converter

In short Urea Nitrogen (BUN) is reported in mg/dL in some countries and mmol/L in others, and the two are related by a fixed factor: 1 mg/dL = 0.356972 mmol/L, so to go the other way you divide by 2.80134. 10 mg/dL BUN is 3.6 mmol/L urea; 20 mg/dL BUN is 7.1 mmol/L urea; 40 mg/dL BUN is 14.3 mmol/L urea. The factor is not arbitrary — it comes from the molar mass, because the conversion counts the two nitrogen atoms in urea, 28.01 g/mol, not the whole urea molecule, and that is why every analyte has its own factor rather than one shared conversion. This is not a unit conversion at all — it is a change of substance. American labs report the *nitrogen* in urea; almost everyone else reports *urea*. Urea contains two nitrogen atoms out of a molar mass of 60.06, so BUN in mg/dL converts to urea in mmol/L by 0.357, and anyone treating the two names as the same measurement in different units will be out by a factor of 2.14. This converts units. It does not interpret results, does not compare your value against a reference interval, and is not a substitute for the clinician who ordered the test — reference intervals differ between laboratories, methods and populations.