A normal fasting blood sugar level is 70 to 99 mg/dL for adults without diabetes. That number shifts throughout the day based on when and what you eat, your activity level, and stress. Understanding where the key thresholds fall helps you interpret lab results and spot early warning signs of prediabetes or diabetes.
Fasting Blood Sugar Ranges
Fasting blood sugar is measured after you haven’t eaten for at least eight hours, which is why it’s typically drawn first thing in the morning. The ranges break down into three categories:
- Normal: 70 to 99 mg/dL (3.9 to 5.5 mmol/L)
- Prediabetes: 100 to 125 mg/dL (5.6 to 6.9 mmol/L)
- Diabetes: 126 mg/dL (7.0 mmol/L) or higher on more than one test
A single high reading doesn’t automatically mean diabetes. Illness, poor sleep, and stress can all push fasting glucose above its usual level temporarily. That’s why a diabetes diagnosis requires elevated results on at least two separate occasions.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal and typically peaks about 60 to 90 minutes later. In people without diabetes, it rarely climbs above 140 mg/dL and returns to pre-meal levels within two to three hours. If your blood sugar stays above 140 mg/dL two hours after eating, that’s a sign your body is struggling to process glucose efficiently.
The size and composition of your meal matters. A plate of white rice will spike your blood sugar faster and higher than a meal with protein, fat, and fiber, even if the calorie counts are similar. This is why post-meal readings can vary widely from day to day in the same person.
A1C: The Bigger Picture
While a fasting test captures a single moment, the A1C test reflects your average blood sugar over the previous two to three months. It measures the percentage of your red blood cells that have glucose attached to them. The ranges are:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
The A1C is useful because it isn’t affected by what you ate the night before or whether you slept poorly. It smooths out the daily ups and downs and gives a more reliable picture of long-term blood sugar control. Some conditions that affect red blood cells, like anemia or sickle cell disease, can make A1C results less accurate.
When Blood Sugar Drops Too Low
Blood sugar below 70 mg/dL is considered low, a condition called hypoglycemia. Symptoms include shaking, sweating, a fast heartbeat, dizziness, irritability, and sudden intense hunger. Most people notice these warning signs early enough to eat or drink something sugary and recover within minutes.
Below 54 mg/dL is classified as severely low. At that level, symptoms become more dangerous: confusion, difficulty walking, blurred vision, and in some cases seizures or loss of consciousness. Severe hypoglycemia is most common in people taking insulin or certain diabetes medications, but it can occasionally happen in people without diabetes after prolonged fasting or heavy exercise.
Ranges During Pregnancy
Pregnancy changes how your body handles insulin, so blood sugar targets are tighter. Most pregnant people are screened for gestational diabetes between 24 and 28 weeks with a one-hour glucose challenge test. A result below 140 mg/dL is normal. If you score 140 or above, you’ll move on to the more detailed three-hour glucose tolerance test, which checks blood sugar at four time points:
- Fasting: below 95 mg/dL
- One hour: below 180 mg/dL
- Two hours: below 155 mg/dL
- Three hours: below 140 mg/dL
If at least two of those four readings come back elevated, the diagnosis is gestational diabetes. This condition usually resolves after delivery, but it does increase the risk of developing type 2 diabetes later in life.
Children and Infants
Normal blood sugar ranges are slightly different for young children. Infants typically run between 40 and 90 mg/dL, which is lower than the adult range. Children under two generally fall between 60 and 100 mg/dL. By school age, children’s normal ranges closely match adult values. The lower end of normal in infants can look alarming compared to adult numbers, but their bodies are adapted to function at those levels.
Older Adults
Blood sugar targets for adults over 65 are often more flexible than for younger people. The risk of a dangerous low blood sugar episode increases with age, and a severe drop can cause falls, confusion, or hospitalization. For this reason, providers sometimes set slightly higher targets for older adults, especially those managing multiple health conditions or taking several medications. There’s no single set of numbers that applies to every older adult.
How Blood Sugar Is Measured
The traditional finger-prick glucometer gives you a blood sugar reading from a small drop of blood. It’s accurate, inexpensive, and widely available, but it only shows your level at the exact moment you test. If you want to see how your blood sugar moves throughout the day, you’d need to prick your finger many times.
Continuous glucose monitors (CGMs) solve that problem. A small sensor inserted just under the skin, usually on the upper arm, samples glucose every minute and records a reading every 15 minutes. Some models push data to your phone in real time, while others require you to scan the sensor. CGMs are especially useful for spotting overnight lows or post-meal spikes you’d miss with occasional finger pricks. Some newer models are accurate enough to base insulin dosing decisions on without a confirmatory finger stick.
One important detail: CGMs measure glucose in the fluid between your cells, not directly in your blood. This means CGM readings can lag a few minutes behind a finger-prick reading, particularly when blood sugar is changing rapidly.
mg/dL vs. mmol/L
If you’ve seen blood sugar reported in unfamiliar units, it’s likely because different countries use different measurement systems. The United States uses mg/dL, while the UK, Canada, Australia, and most of Europe use mmol/L. To convert, divide mg/dL by 18. So a fasting reading of 90 mg/dL equals 5.0 mmol/L. For people without diabetes, the typical range in mmol/L terms is 4 to 6 mmol/L.