From Wikipedia ( https://en.wikipedia.org/wiki/Blood_sugar_level )
Units[edit]
The international standard way of measuring blood glucose levels is in terms of a molar concentration, measured in mmol/L (millimoles per litre; or millimolar, abbreviated mM). In the United States, Germany and other countries mass concentration is measured in mg/dL (milligrams per decilitre).[4]
Since the molecular weight of glucose C6H12O6 is 180, the difference between the two units is a factor of 18, so that 1 mmol/L of glucose is equivalent to 18 mg/dL.[5]