Blood sugar values appear in two units depending on where you are: mg/dL (milligrams per deciliter) used in the US and Germany, and mmol/L (millimoles per liter) used in the UK, Canada, Australia, and most of the world.
This guide explains how to convert between units, what the reference ranges mean, and how to interpret your reading as fasting or postprandial.
Conversion Formula
Blood sugar converts between units using a fixed factor based on the molecular weight of glucose (180.18 g/mol):
| Direction | Formula |
|---|---|
| mg/dL → mmol/L | mmol/L = mg/dL ÷ 18.018 |
| mmol/L → mg/dL | mg/dL = mmol/L × 18.018 |
Example
A fasting blood sugar of 95 mg/dL equals 5.27 mmol/L (95 ÷ 18.018 ≈ 5.27).
Fasting Blood Sugar Reference Ranges
Fasting blood sugar is measured after at least 8 hours without eating. It is the primary value for diagnosing diabetes and prediabetes.
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal | < 100 | < 5.6 |
| Prediabetes | 100 – 125 | 5.6 – 6.9 |
| Diabetes | ≥ 126 | ≥ 7.0 |
Source: American Diabetes Association (ADA) Standards of Care 2024.
Postprandial Blood Sugar Reference Ranges
Postprandial blood sugar is measured 2 hours after a meal. It shows how well the body processes carbohydrates and can be elevated even when fasting values are still normal.
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal | < 140 | < 7.8 |
| Prediabetes | 140 – 199 | 7.8 – 11.0 |
| Diabetes | ≥ 200 | ≥ 11.1 |
Fasting vs. Postprandial
Both measurements reveal different aspects of blood sugar regulation:
- Fasting shows baseline pancreatic function and insulin resistance at rest.
- Postprandial shows the response to carbohydrates and is often elevated earlier than fasting values.
- Elevated postprandial values with normal fasting values can indicate prediabetes.
Relationship to HbA1c
While blood sugar gives a snapshot, HbA1c reflects the average blood sugar over the past 2–3 months. Both tests together provide the most complete picture of glucose metabolism.
An HbA1c of 6.5% corresponds to an estimated average glucose of approximately 140 mg/dL (7.8 mmol/L).
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Open Blood Sugar Converter →Frequently Asked Questions
Why are there two different units?
Different countries adopted different measurement systems historically. The US and Germany use mg/dL, while most other countries use mmol/L. Modern glucose meters often support both units.
Can a single reading diagnose diabetes?
No. A single elevated reading alone is not sufficient for diagnosis. The ADA requires at least two abnormal measurements on different days, or an oral glucose tolerance test. Always consult a doctor.
What affects blood sugar levels?
Meals (especially carbohydrates), physical activity, stress, poor sleep, medications, and illness can all significantly affect blood sugar in the short term. Standardized measurement conditions are important for reliable readings.