What are normal blood sugar levels for adults?

A normal, randomly checked blood glucose level in adults is between 80 and 120 milligrams per deciliter of blood before meals or between 100 and 140 milligrams per deciliter of blood right before bedtime, states WebMD. A normal fasting blood glucose level is any number below 100 milligrams per deciliter.

A blood glucose test is a blood test that measures the concentration of glucose, or sugar, in a patient's bloodstream, states WebMD. Glucose is derived from the foods that patients eat, and it is used by every cell in the human body for energy. Patients who have diabetes are unable to properly utilize glucose and tend to have higher blood sugar levels than patients without diabetes.