Blood sugar level (or blood sugar concentration) is the amount of glucose (a source of energy) present in your blood at any given time. A normal blood glucose level for a healthy person is somewhere between 72 mg/dL (3.8 to 4 mmol/L) and 108 mg/dL (5.8 to 6 mmol/L).It, of course, depends on every individual alone.or children between the age of 6 and 12, before eating, blood sugar levels should be between 90 mg/dL (5 mmol/L) and 180 mg/dL (10 mmol/L). Before sleep values should be between 100 mg/dL (5.5 mmol/L) and 180 mg/dL (10 mmol/L).