WebMD offers a chart of the target blood sugar levels for adults 20 years of age and older with diabetes. The chart indicates the ideal ranges for adults when fasting, before and after meals, prior to exercise and at bedtime.
Target blood sugar levels for diabetics when no meals were consumed in the previous eight hours should be less than 100 mg/dL, notes WebMD. Sugar levels before meals should be 70 to 130 mg/dL, while after-meal readings within 1 to 2 hours should be less than 180 mg/dL. Prior to exercise, blood sugar should be at least 100 mg/dL in individuals taking insulin; nighttime readings before bed should be 100 to 140 mg/dL, recommends WebMD.