kg, g, mg, ug, ng are all weight units, and the conversion relationship between them is: 1kg = 1kg = 1000g, 1g = 1000mg, 1mg = 1000ug, 1ug = 1000ng. l and ml are both volume units, and the conversion factor between them is 1L = 1000ml. 1ug/L is 1000ml containing some substance 1ug, 1ug = 1000ng, which is 1000ml containing some substance 1000ng. Therefore, the conversion factor between ug/L and ng/ml is 1. For example, if the concentration of a substance is 5ug/L, it is equivalent to 5ng/ml. .