What Is Blood Sugar (Blood Glucose)?

Blood sugar (blood glucose) is the amount of glucose present in the bloodstream at any given moment. Glucose comes primarily from carbohydrates in food and is the body's main source of energy. The hormone insulin — produced by beta cells in the pancreas — allows cells to absorb glucose from the blood. When this process is impaired, blood glucose levels become chronically elevated, leading to prediabetes and eventually type 2 diabetes.

Why it matters: Chronically elevated blood sugar damages blood vessels and nerves, leading to diabetes complications including heart disease, kidney failure, blindness, and neuropathy. Regular monitoring is the only way to catch abnormal levels early.

Complete Blood Sugar Reference Chart

FASTING 2-HR POST-MEAL A1C (HbA1c) Normal: <100 mg/dL <140 mg/dL <5.7% Prediabetes: 100–125 140–199 5.7–6.4% Diabetes: ≥126 mg/dL ≥200 mg/dL ≥6.5% mmol/L conversions: Normal fasting: <5.6 mmol/L Prediabetes: 5.6–6.9 mmol/L Diabetes: ≥7.0 mmol/L
38MAmericans with diabetes
96Mhave prediabetes
80%prediabetes undiagnosed
7.0%A1C target for most diabetics

Fasting Blood Sugar Levels Explained

Fasting blood sugar is measured after at least 8 hours without food or drink (except water). It is the most commonly used initial screening test for diabetes.

  • Below 100 mg/dL (5.6 mmol/L) — Normal: Your body is effectively managing blood glucose. Continue healthy habits to maintain this level.
  • 100–125 mg/dL (5.6–6.9 mmol/L) — Prediabetes (Impaired Fasting Glucose): Your fasting blood sugar is above normal but not yet diabetic. Lifestyle intervention now can prevent or delay diabetes onset by up to 58% according to the Diabetes Prevention Program (DPP).
  • 126 mg/dL (7.0 mmol/L) or above — Diabetes: Requires confirmation with a second test on a separate day. This level indicates your body is not producing enough insulin or has developed significant insulin resistance.

Blood Sugar After Eating (Postprandial)

Postprandial glucose is measured 1–2 hours after beginning a meal. Blood sugar naturally peaks at around 60–90 minutes after eating, then returns to normal. Understanding postprandial levels helps identify how specific foods affect your individual glucose response.

  • Below 140 mg/dL (7.8 mmol/L) at 2 hours — Normal: A healthy glucose response. The pancreas produced adequate insulin to manage the carbohydrate load.
  • 140–199 mg/dL (7.8–11.0 mmol/L) at 2 hours — Prediabetes: Impaired glucose tolerance. Your body is struggling to manage post-meal glucose effectively.
  • 200 mg/dL (11.1 mmol/L) or above at 2 hours — Diabetes: Highly elevated post-meal glucose indicative of significant insulin dysfunction.

Reducing postprandial spikes is one of the most impactful things you can do for blood sugar control. Taking a 10-minute walk after meals, choosing lower-glycemic foods, increasing fiber and protein intake, and eating in smaller portions all significantly reduce post-meal glucose peaks.

A1C (HbA1c) Chart — 3-Month Average

A1C measures the percentage of hemoglobin with attached glucose, reflecting average blood sugar over approximately 2–3 months. It is the gold-standard diagnostic and monitoring test for diabetes.

A1C Level Average Blood Sugar (eAG) Classification <5.7% <117 mg/dL (<6.5 mmol/L) Normal 5.7–6.4% 117–137 mg/dL (6.5–7.6) Prediabetes 6.5–6.9% 140–154 mg/dL (7.8–8.6) Diabetes (controlled) 7.0–7.9% 154–183 mg/dL (8.6–10.2) Diabetes (suboptimal) 8.0–8.9% 183–212 mg/dL (10.2–11.8) Diabetes (poorly controlled) ≥9.0% ≥212 mg/dL (≥11.8) Diabetes (very poorly controlled)

The ADA target for most non-pregnant adults with diabetes is A1C below 7.0%. More stringent targets (below 6.5%) may be appropriate for younger, healthier individuals. Less stringent targets (below 8.0%) are recommended for elderly patients or those with history of severe hypoglycemia.

Understanding Prediabetes — A Critical Window

Prediabetes is not a guaranteed path to diabetes — it is a reversible condition. The landmark Diabetes Prevention Program study showed that intensive lifestyle intervention (7% weight loss + 150 minutes/week of moderate exercise) reduced progression from prediabetes to type 2 diabetes by 58% over 3 years. For adults over 60, the reduction was 71%. This is why early detection matters enormously.

If you have prediabetes, get retested every 6–12 months and prioritize: losing 5–7% of body weight if overweight, increasing physical activity, reducing refined carbohydrates and added sugars, and building more fiber into your diet.

Diabetic Blood Sugar Range — Management Targets

For people already diagnosed with type 2 diabetes, the ADA recommends the following targets:

  • Fasting/before meals: 80–130 mg/dL (4.4–7.2 mmol/L)
  • 1–2 hours after meals: Below 180 mg/dL (10.0 mmol/L)
  • A1C: Below 7.0% for most adults
  • Time In Range (CGM target): Above 70% of readings between 70–180 mg/dL
Hypoglycemia warning: Blood sugar below 70 mg/dL (3.9 mmol/L) is hypoglycemia — a medical emergency for people on insulin or sulfonylureas. Symptoms include shakiness, sweating, confusion, rapid heartbeat, and hunger. Treat immediately with 15g of fast-acting carbohydrates (4 glucose tablets, 4 oz juice, or regular soda). Retest after 15 minutes.