Normal Blood Sugar Levels Chart — Fasting, Postprandial, and HbA1c

What Blood Sugar Conversion Does

Blood glucose concentration can be reported in two different units depending on your location: milligrams per deciliter (mg/dL), which is standard in the United States, and millimoles per liter (mmol/L), which is used in most other countries including the UK, Canada, Australia, and Europe. This converter allows instant, accurate conversion between both units so that you can interpret lab results, glucose meter readings, or medical advice regardless of which unit is used.

The conversion is based on the molar mass of glucose — the weight of one mole of glucose molecules. Glucose has a molecular formula of C₆H₁₂O₆, giving it a molar mass of 180.182 g/mol. This fundamental chemical constant serves as the bridge between the mass-based unit (mg/dL) and the molar-based unit (mmol/L).

Conversion Formulas

Worked Example

Suppose your fasting blood glucose reading is 126 mg/dL. To convert to mmol/L: 126 ÷ 18.0182 = 7.0 mmol/L. This is the diagnostic threshold for diabetes according to the American Diabetes Association. Conversely, if a lab report shows a value of 5.6 mmol/L, convert to mg/dL: 5.6 × 18.0182 = 100.9 mg/dL ≈ 101 mg/dL. This is the upper end of the normal fasting range.

FAQ-Style Explanations

Why is the conversion factor 18.0182 and not exactly 18? The exact factor is derived from the molar mass of glucose (180.182 g/mol) divided by 10 (since 1 dL = 0.1 L). Many people use 18 as a quick approximation, but for clinical accuracy, especially at higher glucose levels, the full factor of 18.0182 should be used.

Which unit should I use? Use whichever unit your local healthcare system uses. In the US, all labs and glucose meters report in mg/dL. In most other countries, mmol/L is standard. The converter helps you move between the two seamlessly if you travel, consult international specialists, or read research from other countries.

Can I use this conversion for HbA1c? No. HbA1c (glycated hemoglobin) is a different measurement that represents average blood sugar over 2–3 months. It is reported as a percentage or in mmol/mol and requires a different conversion formula.

Known Limitations

• This converter provides accurate unit conversion but does not interpret your blood sugar levels — always consult a healthcare provider for medical interpretation.
• The conversion factor is based on the molecular weight of glucose in its standard form. Extremely rare laboratory variations in measurement techniques may introduce minor discrepancies at the thousandths place.
• Some glucose meters report in whole numbers only (e.g., 100 mg/dL rather than 100.0 mg/dL), which can introduce rounding differences of ±1 mg/dL or ±0.1 mmol/L.
• The reference ranges shown are general guidelines. Individual targets may vary based on age, diabetes type, pregnancy status, and other medical factors.

Reference Ranges

Fasting Blood Glucose Levels

Fasting blood glucose is measured after at least 8 hours without food or caloric drink (water is permitted), typically drawn in the morning before breakfast. It reflects your baseline blood sugar level and is one of the primary screening tests for diabetes. The American Diabetes Association (ADA) classifies fasting blood glucose as normal below 100 mg/dL (5.6 mmol/L), prediabetes in the range of 100 to 125 mg/dL (5.6 to 6.9 mmol/L), and diabetes at 126 mg/dL (7.0 mmol/L) or higher on two separate occasions. Values below 70 mg/dL (3.9 mmol/L) indicate hypoglycemia and require attention, especially in people with diabetes on insulin or sulfonylurea medications. Fasting glucose is the most widely used screening test because it is simple, inexpensive, and reproducible, though it has lower sensitivity than the oral glucose tolerance test (OGTT) for detecting early prediabetes.

Two-Hour Postprandial Blood Glucose

Postprandial (after-meal) blood glucose is measured 2 hours after the first bite of a meal and reflects how effectively your body handles the glucose load from food. For non-diabetic individuals, blood glucose typically peaks 30 to 60 minutes after eating and returns to below 140 mg/dL (7.8 mmol/L) by the 2-hour mark. The ADA defines postprandial blood sugar as normal below 140 mg/dL (7.8 mmol/L), prediabetes (impaired glucose tolerance, IGT) at 140 to 199 mg/dL (7.8 to 11.0 mmol/L), and diabetes at 200 mg/dL (11.1 mmol/L) or higher. Postprandial hyperglycemia is an independent predictor of cardiovascular disease and may precede fasting hyperglycemia by several years in the progression to diabetes, making it an important early warning marker. Self-monitoring of postprandial glucose with a home glucometer is increasingly recommended for people with prediabetes and diabetes to identify dietary patterns that cause excessive glucose excursions.

HbA1c — The 3-Month Average

Hemoglobin A1c (HbA1c) measures the percentage of hemoglobin molecules in your blood that have glucose attached to them. Because red blood cells live for approximately 120 days, HbA1c reflects average blood glucose over the preceding 2 to 3 months, making it the gold standard for monitoring long-term glycemic control. The ADA defines HbA1c as normal below 5.7 percent, prediabetes at 5.7 to 6.4 percent, and diabetes at 6.5 percent or higher. Unlike fasting and postprandial glucose, HbA1c does not require fasting and is not affected by short-term fluctuations in diet or stress, which makes it the most reliable single test for diabetes diagnosis and ongoing management. For individuals with well-controlled diabetes, the treatment target is typically below 7.0 percent, though tighter targets (6.5 percent or lower) may be appropriate for younger patients and more relaxed targets (7.5 to 8.0 percent) for older patients with multiple comorbidities.

Factors That Affect Blood Sugar Readings

Several factors can temporarily affect blood sugar readings and should be considered when interpreting results. Physical stress from illness, surgery, or injury raises blood glucose through increased cortisol and adrenaline secretion, and elevated readings during acute illness do not necessarily indicate new-onset diabetes. Certain medications — particularly corticosteroids, thiazide diuretics, some antipsychotics, and statins — can elevate fasting and postprandial glucose. Dehydration concentrates blood glucose and can produce falsely elevated readings. For HbA1c specifically, conditions that alter red blood cell turnover — such as iron-deficiency anemia, vitamin B12 deficiency, hemolytic anemia, and recent blood transfusion — can artificially lower HbA1c, while conditions that prolong red blood cell survival can artificially raise it. Athletes who engage in intense training may also have slightly lower HbA1c values. Always interpret blood sugar results in clinical context, and repeat borderline results rather than making decisions based on a single reading.

When to Get Blood Sugar Tested

The ADA recommends diabetes screening for all adults aged 35 and older, regardless of risk factors, at least every 3 years. Earlier and more frequent screening is recommended for individuals with overweight or obesity (BMI 25 or higher), a first-degree relative with diabetes, high-risk ethnic background (African American, Hispanic, Native American, Asian American, Pacific Islander), a history of gestational diabetes, hypertension (blood pressure above 140/90 mmHg or on antihypertensive treatment), HDL cholesterol below 35 mg/dL (0.9 mmol/L) or triglycerides above 250 mg/dL (2.8 mmol/L), physical inactivity, or a history of cardiovascular disease. Prediabetes (identified by fasting glucose 100 to 125 mg/dL, HbA1c 5.7 to 6.4%, or OGTT 140 to 199 mg/dL) should be rechecked annually, and lifestyle intervention during this stage has been shown to reduce the risk of progressing to diabetes by 58 percent in the landmark Diabetes Prevention Program trial.