Blood Glucose: Normal Range, Levels Chart, and What Your Number Means

Blood glucose is the concentration of sugar circulating in your blood at the moment the sample is taken. Every cell in your body runs on it, and your body works hard to keep it in a narrow range — roughly 70 to 140 mg/dL (3.9 to 7.8 mmol/L) in a healthy adult, depending on the time since the last meal.

Three hormones do most of the work. After you eat, the pancreas releases insulin, which moves glucose into cells and tells the liver to stop releasing its own. Between meals, glucagon does the opposite — tells the liver to put glucose back into circulation. Cortisol and adrenaline override both during stress, pushing glucose up regardless of meals. When any part of this system is off — too little insulin, cells that don't respond to it, too much cortisol — blood glucose drifts outside the normal range.

A single glucose reading tells you what the system is doing right now. It doesn't tell you what it's been doing on average, which is what HbA1c is for.

Reference ranges by time of day (non-diabetic adult)

• Fasting (8+ hours): 70–99 mg/dL (3.9–5.5 mmol/L)
• 1 hour after a meal: typically under 140 mg/dL; peaks of 140–160 are common in healthy adults
• 2 hours after a meal: under 140 mg/dL (7.8 mmol/L)
• Random (any time of day): usually 80–140 mg/dL
• Bedtime: 100–140 mg/dL

Diagnostic cutoffs (non-pregnant adult)

These are the numbers clinicians use to diagnose prediabetes and diabetes. They come from the ADA's 2025 Standards of Care.

• Fasting glucose: normal < 100, prediabetes 100–125, diabetes ≥ 126 (confirmed on a separate day)
• Random glucose with symptoms: diabetes ≥ 200 mg/dL
• OGTT 2-hour: normal < 140, prediabetes 140–199, diabetes ≥ 200
• HbA1c: normal < 5.7%, prediabetes 5.7–6.4%, diabetes ≥ 6.5%

Targets for people with diabetes (ADA, individualized)

These are treatment goals, not diagnostic thresholds, and your clinician may set them differently based on age, comorbidities, and hypoglycemia risk.

• Before meals: 80–130 mg/dL
• 1–2 hours after start of meal: < 180 mg/dL
• A1c: < 7% for most adults; < 7.5–8.0% for older adults with comorbidities
• Time in Range (CGM users): ≥ 70% of time between 70 and 180 mg/dL

The context matters more than the number

A reading of 160 an hour after a big bowl of pasta is not the same finding as 160 six hours after eating. Before reacting to a high number, answer two questions: when did I last eat, and what did I eat?

100–125 fasting, or 140–199 at two hours post-meal / post-OGTT

This is the prediabetes band. It usually produces no symptoms. The clinical goal is to catch it here, because the evidence for prevention is strong: the CDC's Diabetes Prevention Program (5–7% weight loss, 150 minutes of moderate activity per week) cuts the rate of progression to type 2 diabetes by about 58% over three years.

≥ 126 fasting, or ≥ 200 at two hours post-OGTT, or ≥ 200 random with symptoms

This meets the diabetes threshold. A random reading ≥ 200 with classic symptoms (thirst, frequent urination, unexplained weight loss, blurred vision) is diagnostic on its own. Otherwise, confirmation requires a second abnormal test on a different day.

Very high readings (≥ 250 mg/dL)

In someone with type 1 diabetes, this is the range where diabetic ketoacidosis (DKA) becomes a risk — particularly if ketones are present, along with nausea, abdominal pain, fruity breath, or rapid breathing. DKA is a medical emergency. In someone with type 2, very high readings (600+) can progress to hyperosmolar hyperglycemic state (HHS), another emergency. Either way, a reading this high with symptoms is not something to "watch at home."

High readings that aren't diabetes

• Eating (obvious, but commonly missed when labeled "fasting")
• Stress, illness, infection
• Corticosteroids — prednisone raises glucose within days of starting
• Thiazides, atypical antipsychotics, beta-blockers, tacrolimus
• Dawn phenomenon (overnight cortisol/growth hormone rise)
• Short or poor sleep the night before
• Consumer meter error — expect ±10–15% compared to a lab draw

Hypoglycemia is generally defined at three levels:

• Level 1: glucose < 70 mg/dL. An alert value. Fast-acting carbohydrate (15g of juice, glucose tablets, or regular soda) is the standard response. Re-check in 15 minutes.
• Level 2: glucose < 54 mg/dL. Clinically significant. More likely to cause symptoms — shakiness, sweating, confusion, fast heart rate.
• Level 3: any glucose with altered mental status or seizure. Severe. May require glucagon or emergency care.

Low glucose in people on insulin or sulfonylureas is by far the most common cause. Outside of that, low readings in non-diabetics are uncommon and usually merit a workup — particularly when they're repeated or symptomatic.

One caveat: meters read imprecisely at the extremes. A meter reading of 64 may correspond to a lab value anywhere from 54 to 74. If you feel fine and the reading looks low, re-test on a different finger with clean hands before treating.

A single glucose reading is a snapshot of one moment. It's useful for safety (catching hypoglycemia, ruling out severe hyperglycemia) but limited for understanding your metabolic baseline. For that, you want one of two things:

• A series of fasting readings over weeks and months. The median is what matters. A healthy adult's fasting glucose can bounce between 88 and 104 across tests without anything having changed.
• HbA1c. It averages the last 2–3 months in one number and is less sensitive to day-to-day noise.

If you use a continuous glucose monitor, the most useful number is usually Time in Range — the percentage of the day your glucose stays between 70 and 180 mg/dL. Two people with an A1c of 7% can have very different time in range, and the one with less time in range is the one with more glycemic variability, which matters clinically.

A single reading almost never needs an urgent visit. The following patterns do:

• Multiple fasting readings ≥ 126 mg/dL, or an HbA1c ≥ 6.5% — confirms a diabetes diagnosis.
• Any glucose ≥ 250 mg/dL with nausea, vomiting, abdominal pain, rapid breathing, fruity breath, or confusion — possible DKA. Emergency care.
• Glucose ≥ 600 mg/dL with or without symptoms — possible HHS. Emergency care.
• Repeated glucose < 70 mg/dL, especially with symptoms (shakiness, sweating, confusion) — needs evaluation, whether you take glucose-lowering medication or not.
• Any loss of consciousness or seizure in someone with diabetes — call emergency services.

• HbA1c (4548-4) — 2–3 month average glucose. Less sensitive to day-to-day noise; the gold standard for diagnosis and management.
• Fasting glucose (1558-6) — same measurement, specifically after an 8+ hour fast. The classic screening test.
• OGTT (1521-4) — 2-hour reading after a 75g glucose drink. Used to diagnose gestational diabetes and to resolve borderline A1c/fasting glucose.
• Fructosamine — 2–3 week average glucose. Used when A1c is unreliable (hemoglobin variants, recent transfusion, pregnancy).
• Fasting insulin — used with fasting glucose to estimate insulin resistance (HOMA-IR).
• C-peptide — measures how much insulin your pancreas is producing. Relevant in distinguishing type 1 from type 2 diabetes.