A1C to average glucose, plus mg/dL ↔ mmol/L converter.
Two small tools in one place. Translate an A1C percentage into the average glucose number you see on a meter or CGM, and convert glucose readings between mg/dL and mmol/L. Everything runs in your browser. Nothing is sent anywhere, nothing is stored.
Formula: average glucose (mg/dL) = 28.7 × A1C − 46.7. Then mmol/L = mg/dL ÷ 18. This is the published ADAG (A1C-Derived Average Glucose) equation used by the American Diabetes Association.
mg/dL = mmol/L × 18. The factor 18 is the value conventionally used in clinical practice worldwide. Round mmol/L to one decimal, mg/dL to the nearest integer.
What is A1C / HbA1c?
A1C, sometimes written HbA1c, is a single percentage that estimates your average blood sugar over roughly the last two to three months. The number itself is the share of your red blood cells that have sugar molecules attached. Because red blood cells live about 90 days, the percentage gives a useful long-view snapshot of how your glucose has been behaving, in a way no single fingerstick can.
Your doctor uses A1C as one of the main yardsticks for diagnosing prediabetes (around 5.7 to 6.4 percent) and type 2 diabetes (6.5 percent and up). It is also the standard way that diabetes care progress gets tracked over time.
What is estimated average glucose (eAG)?
Your A1C is a percentage, but the glucose you see on a meter or a CGM is a real-world number in mg/dL (or mmol/L outside the US). Estimated average glucose, or eAG, is simply the A1C translated back into those everyday units. It is the same information, just in language you actually recognize from your sensor app.
This tool uses the medically accepted equation: eAG in mg/dL = 28.7 × A1C − 46.7, then divides by 18 to get mmol/L. That equation comes from the ADAG (A1C-Derived Average Glucose) study and is the formula the American Diabetes Association uses.
For background on the underlying numbers your sensor shows, see our beginner article on how to read CGM glucose numbers, and our pillar What is a CGM? A plain English guide.
Why are there two units?
Glucose is the same molecule everywhere, but different countries report it using different units. mg/dL (milligrams per deciliter) is the convention in countries such as the United States, Germany, France, and Japan. mmol/L (millimoles per liter) is the convention in countries such as the UK, much of Europe, Canada, and Australia. Both describe the same thing, just on different scales. The factor 18 converts between them in clinical practice.
If you have ever stared at an app set to the "wrong" unit and felt your numbers looked unfamiliar, this is why. Switching units does not change your glucose; it just changes the label on the same value.
This tool is educational. The eAG equation is a population average, which means your personal average glucose can differ from the estimate, particularly if you have a condition that affects red blood cells (such as anemia, certain hemoglobin variants, recent transfusions, or pregnancy). Treat the result as a useful estimate, not an exact measurement, and discuss your actual numbers with your healthcare provider.
Common questions
Is this a diagnosis?
No. This tool gives you general reference information using a published medical formula. A diagnosis of prediabetes or diabetes is made by a healthcare provider using clinical lab results, often confirmed on a second test. Always discuss your numbers with your provider.
Which unit should I use, mg/dL or mmol/L?
Use whichever unit your country and your healthcare provider use. The numbers describe the same thing; the only difference is the scale. If your sensor app is set to a unit you do not recognize, switch it in the app settings.
How accurate is the A1C to glucose estimate?
The formula is the medically accepted ADAG standard. It is a population average, so your personal average glucose can differ from the estimate by a meaningful amount, particularly if you have any condition that affects red blood cells. Treat the result as a useful estimate, not an exact measurement. [VERIFY: stat, optional plus/minus mg/dL range from the ADAG paper if you want to quote one]
Why does this tool work without an account or login?
All calculation happens in your browser using a few lines of plain JavaScript. We never send your value anywhere, never store it, and never log it. Refresh the page and it is gone.
Where does the formula come from?
The A1C to estimated average glucose equation used here is from the ADAG study published in Diabetes Care in 2008. [VERIFY: citation, fill in the exact Nathan DM et al. 2008 reference] It is the formula the American Diabetes Association uses to translate A1C into mg/dL and mmol/L.
For deeper reading: NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases) on continuous glucose monitoring and American Diabetes Association (ADA).
References
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Continuous glucose monitoring. niddk.nih.gov/health-information/diabetes/overview/managing-diabetes/continuous-glucose-monitoring.
- American Diabetes Association. diabetes.org. The eAG equation used in this tool is the ADAG (A1C-Derived Average Glucose) formula adopted by the ADA.
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ, for the A1c-Derived Average Glucose Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care, 2008. [VERIFY: citation, fill in exact volume, issue, and page numbers before publishing]
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