Blood sugar is reported in mg/dL (common in the US) or mmol/L (common in the UK, Canada, and Europe). As a general guide for people without diabetes, fasting glucose is typically under 100 mg/dL (5.6 mmol/L), and the prediabetes range is roughly 100 to 125 mg/dL (5.6 to 6.9 mmol/L).
Readings shift throughout the day depending on meals, activity, stress, illness, and sleep, so a single number is less meaningful than the overall pattern. People with diabetes are usually given individualised targets, which may differ from the general population, especially for older adults or during pregnancy.
These figures are general reference points, not a diagnosis or a personal target. Ask your doctor or pharmacist what range is right for you, particularly if you take glucose-lowering medication.