Blood urea nitrogen is a test that measures the amount of urea nitrogen found in blood. Normal human adult blood should contain between 6 and 20 mg of urea nitrogen per 100 ml (6–20 mg/dL) of blood. Normal blood urea levels are between 20 and 50  mg/dL. There might be slight differences between different laboratories. The conversion between both is that blood urea is approximately 2.14 times blood nitrogen bound to urea.

Dear Punuru 

Chemical formula of urea is ( NH2 )2  >C=O  i.e.  Molecular weight of urea is 60 while nitrogen in it is 28 . 60/28 = 2.14 , so the conversion is blood urea nitrogen × 2.14 = blood urea , a calculative value . Blood urea Nitrogen normal value  is  6 and 20 mg  per 100 ml while normal value of blood urea is  20 and 50  mg 100 ml. 

Thanks for your answers Dr. Koltai and Dr. Sharma 

You can view it as nitrogen being a subset of urea. Nitrogen is part of urea with molecular weight of 28 while molecular weight of urea is 60. Therefore urea÷nitrogen = 60÷28= 2.14. Hence to convert urea to BUN divide by 2.14 and vice versa

Serum Urea (mg/dl) = BUN X 2.14 (mg/dl).