Enter a fasting, random, or 2-hour post-meal blood glucose reading to see which ADA diagnostic category it falls into, shown in both mg/dL and mmol/L.
A fasting glucose test measures blood sugar after at least 8 hours without food, showing your baseline glucose control. A 2-hour post-meal (OGTT) reading measures how well your body clears a glucose load, so its diabetes threshold (200 mg/dL) is higher than fasting's (126 mg/dL) — eating naturally raises blood sugar for a while. A random (casual) reading, taken at any time of day, is the least precise of the three: a result of 200 mg/dL or above only supports a diabetes diagnosis when paired with classic symptoms, and a normal-range random reading does not rule diabetes out. That's why each test type uses a different cut-off.
⚕️ Medical Notice: This calculator is a screening and educational tool only. A single blood glucose reading — however high or low — cannot diagnose diabetes or prediabetes. Diagnosis requires confirmation through repeat testing on a different day, or an HbA1c test, interpreted by your doctor alongside your medical history. If you have concerning symptoms or a result outside the normal range, please consult a qualified healthcare professional.
| Category | Range for this test | Your Status |
|---|
The American Diabetes Association (ADA) sets diagnostic cut-offs for blood glucose depending on which test was used and when it was taken. Because eating raises blood sugar, the threshold for a post-meal test is higher than for a fasting test — a normal fasting reading and a normal post-meal reading sit at very different points on the same glucose curve. The three tables below show the most common test types, each in both mg/dL and mmol/L.
Measured after at least 8 hours with no food or drink other than water, usually first thing in the morning before breakfast.
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal | Under 100 mg/dL | Under 5.6 mmol/L |
| Prediabetes (Impaired Fasting Glucose) | 100–125 mg/dL | 5.6–6.9 mmol/L |
| Diabetes range | 126 mg/dL or above | 7.0 mmol/L or above |
Measured two hours after drinking a standardised 75g glucose solution in a clinical OGTT, or informally around two hours after starting a meal.
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal | Under 140 mg/dL | Under 7.8 mmol/L |
| Prediabetes (Impaired Glucose Tolerance) | 140–199 mg/dL | 7.8–11.0 mmol/L |
| Diabetes range | 200 mg/dL or above | 11.1 mmol/L or above |
Taken at any time of day, regardless of when you last ate. On its own, this is the least precise of the three tests.
| Category | mg/dL | mmol/L |
|---|---|---|
| Below 200 mg/dL | Under 200 mg/dL | Under 11.1 mmol/L |
| 200 mg/dL or above, with classic symptoms | 200 mg/dL or above | 11.1 mmol/L or above |
A blood glucose reading sits alongside how you actually feel. The following is general information, not a checklist for self-diagnosis — seek medical advice if you experience these symptoms, especially if they are severe or sudden.
Hypoglycemia is generally defined as a blood glucose reading under 70 mg/dL (under 3.9 mmol/L). It can develop quickly and needs prompt action.
Blood glucose naturally moves throughout the day, so several everyday factors can shift a single reading without indicating diabetes:
A fasting, random, or OGTT glucose reading is a snapshot of your blood sugar at one moment. HbA1c is a different blood test that reflects your average blood glucose over roughly the past two to three months, by measuring the percentage of red blood cells with sugar attached. The ADA's HbA1c ranges are normal under 5.7%, prediabetes 5.7–6.4%, and diabetes 6.5% or above. Because the two tests measure different things, doctors often use them together for a fuller picture before making a diagnosis.
What is a normal fasting blood sugar level?
A normal fasting blood glucose is under 100 mg/dL (under 5.6 mmol/L), according to American Diabetes Association (ADA) criteria. A fasting reading of 100–125 mg/dL (5.6–6.9 mmol/L) is classified as prediabetes (impaired fasting glucose), and 126 mg/dL (7.0 mmol/L) or above on more than one occasion indicates the diabetes range.
What blood sugar level indicates diabetes?
Diabetes is generally indicated by a fasting glucose of 126 mg/dL (7.0 mmol/L) or above, a 2-hour OGTT reading of 200 mg/dL (11.1 mmol/L) or above, or a random glucose of 200 mg/dL (11.1 mmol/L) or above together with classic symptoms such as excessive thirst or frequent urination. Diagnosis is confirmed by a doctor, usually with a repeat test or an HbA1c.
What is the difference between fasting, random, and OGTT glucose tests?
A fasting test is taken after at least 8 hours without food. A random (casual) test can be taken at any time regardless of meals, so it is the least precise on its own. An OGTT measures glucose 2 hours after drinking a standardised glucose solution, showing how well your body clears sugar after a meal-like load — which is why its diabetes threshold (200 mg/dL) is higher than fasting's (126 mg/dL).
Can one high blood sugar reading mean I have diabetes?
Not on its own. A single elevated reading is a screening result, not a diagnosis. The American Diabetes Association recommends confirming any abnormal result with a repeat test on a different day, or with an HbA1c test, unless blood glucose is very high and accompanied by classic symptoms. Speak with your doctor about any concerning reading.
What is prediabetes?
Prediabetes means your blood glucose is higher than normal but not yet in the diabetes range. On a fasting test this is 100–125 mg/dL (5.6–6.9 mmol/L), sometimes called impaired fasting glucose; on a 2-hour OGTT this is 140–199 mg/dL (7.8–11.0 mmol/L), called impaired glucose tolerance. Prediabetes raises the risk of developing type 2 diabetes and is worth discussing with your doctor.
How do I convert mg/dL to mmol/L for blood sugar?
Divide the mg/dL value by 18.0182 to get mmol/L. For example, 110 mg/dL ÷ 18.0182 = 6.1 mmol/L. To convert the other way, multiply the mmol/L value by 18.0182. mg/dL is the standard unit in the United States, while mmol/L is standard in Australia and most other countries.
What is considered low blood sugar (hypoglycemia)?
Hypoglycemia is generally defined as a blood glucose reading under 70 mg/dL (under 3.9 mmol/L). Symptoms can include shakiness, sweating, a fast heartbeat, sudden hunger, dizziness, or confusion, and can develop quickly. Low blood sugar needs prompt action — follow your doctor's or diabetes educator's advice, and seek urgent care for severe symptoms such as confusion or loss of consciousness.
Why does a random blood sugar reading below 200 mg/dL not rule out diabetes?
A random glucose test only reliably signals diabetes at 200 mg/dL (11.1 mmol/L) or above, and only when combined with classic symptoms. A reading below that threshold could simply reflect when you last ate, so it cannot rule diabetes out on its own. If diabetes is suspected, a fasting glucose test, an OGTT, or an HbA1c test gives a clearer picture.
How is blood sugar different from HbA1c?
A blood glucose reading — fasting, random, or OGTT — is a snapshot of your blood sugar at one moment. HbA1c reflects your average blood glucose over roughly the past 2–3 months by measuring the percentage of red blood cells with sugar attached. Both are used by doctors, often together, to screen for and monitor diabetes and prediabetes.
Is this blood sugar calculator a substitute for medical testing?
No. This calculator is an educational screening tool that shows where a glucose reading falls under published ADA diagnostic ranges. It cannot diagnose diabetes, prediabetes, or any other condition. Only a qualified healthcare professional can interpret your results in the context of your full medical history and order any follow-up testing you may need.