BUN is usually reported in mg/dL in some countries (e.g. United States, Mexico, Italy, Austria, and Germany). Elsewhere, the concentration of urea is reported in SI units as mmol/L.
 represents the mass of nitrogen within urea/volume, not the mass of whole urea. Each molecule of urea has two nitrogen atoms, each having molar mass 14 g/mol. To convert from mg/dL of blood urea nitrogen to mmol/L of urea:
Note that molar concentrations of urea and urea nitrogen are equal, because both nitrogen gas and urea has two nitrogen atoms.
Convert BUN to urea in mg/dL by using following formula:
Where 60 represents MW of urea and 14*2 MW of urea nitrogen.