Enter any one value and the other three update instantly: A1C in percent or mmol/mol, and the estimated average glucose (eAG) it corresponds to in mg/dL or mmol/L. It is built for anyone comparing a lab A1C with day-to-day readings, including CGM users checking sensor data against the lab value.
GMI to A1C: estimate A1C from your CGM average
Wearing a CGM? The glucose management indicator (GMI) converts your sensor average into an A1C-style percentage. Enter the average glucose your CGM app reports for the last 14 to 90 days:
Estimated GMI:
GMI and a lab A1C often disagree. In the study that defined GMI (Bergenstal et al., Diabetes Care 2018), the two matched exactly in 19 percent of people, differed by 0.3 points or more in 51 percent and by 0.5 points or more in 28 percent. Our GMI vs A1C guide explains why, and Sugar Sense shows GMI from your connected CGM in Statistics, free.
How is A1C calculated?
A lab A1C test measures the share of your hemoglobin that has glucose attached. Red blood cells live about three months, so the result reflects your average glucose over roughly the last two to three months, with recent weeks counting more. It is reported in percent in the US and in mmol/mol (IFCC units) in many other countries.
This A1C calculator does not measure anything. It converts. The ADAG study (Nathan et al., Diabetes Care 2008, 507 participants, about 2,700 glucose values each over three months) found that average glucose and A1C sit on a straight line, eAG in mg/dL = 28.7 x A1C - 46.7, and that line runs both ways: A1C = (average glucose + 46.7) / 28.7. Every number on this page comes from those formulas, so an A1C estimated from an average is orientation, never a diagnosis.
Average glucose to A1C
Type your average glucose into the calculator above, or read it off these examples from the ADAG line: 110 mg/dL (6.1 mmol/L) is about 5.5 percent, 126 mg/dL (7.0 mmol/L) about 6.0 percent, 140 mg/dL (7.8 mmol/L) about 6.5 percent and 154 mg/dL (8.6 mmol/L) about 7.0 percent.
One caveat: a meter log of a few readings a day is not a three-month average. Fasting and pre-meal readings usually run lower than the day as a whole, so an A1C estimated from them tends to come out low. A CGM average over 14 to 90 days is much closer to what the lab sees, which is what GMI is built on.
The formulas behind this page
- eAG (mg/dL) = 28.7 x A1C - 46.7, from the ADAG study that defined estimated average glucose. Nathan et al., Diabetes Care 2008
- A1C (%) = (eAG in mg/dL + 46.7) / 28.7, the same ADAG line solved for A1C, which is how the calculator turns an average glucose into an estimated A1C.
- GMI (%) = 3.31 + 0.02392 x mean glucose (mg/dL), from the study that defined the glucose management indicator. Bergenstal et al., Diabetes Care 2018
- IFCC A1C (mmol/mol) = (A1C% - 2.15) x 10.929, the standard conversion between the two A1C reporting systems. In the US, percent results are standardized to the DCCT scale by the National Glycohemoglobin Standardization Program (NGSP).
A1C conversion chart
The A1C conversion chart below lists A1C in percent and mmol/mol with the estimated average glucose in both units, in half-point steps from 4.5 to 14.0, all from the ADAG formula.
| A1C (%) | A1C (mmol/mol) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|---|
| 4.5 | 26 | 82 | 4.6 |
| 5.0 | 31 | 97 | 5.4 |
| 5.5 | 37 | 111 | 6.2 |
| 6.0 | 42 | 125 | 7.0 |
| 6.5 | 48 | 140 | 7.8 |
| 7.0 | 53 | 154 | 8.6 |
| 7.5 | 58 | 169 | 9.4 |
| 8.0 | 64 | 183 | 10.2 |
| 8.5 | 69 | 197 | 10.9 |
| 9.0 | 75 | 212 | 11.7 |
| 9.5 | 80 | 226 | 12.5 |
| 10.0 | 86 | 240 | 13.3 |
| 10.5 | 91 | 255 | 14.1 |
| 11.0 | 97 | 269 | 14.9 |
| 11.5 | 102 | 283 | 15.7 |
| 12.0 | 108 | 298 | 16.5 |
| 12.5 | 113 | 312 | 17.3 |
| 13.0 | 119 | 326 | 18.1 |
| 13.5 | 124 | 341 | 18.9 |
| 14.0 | 130 | 355 | 19.7 |
A1C is only part of the picture: two people with the same A1C can have very different days. Trends over time matter more than any single result. That is why modern guidelines pair it with time in range, explained in our Time in Range guide. Need to switch a single value between units instead? Use the blood sugar unit converter.
Frequently asked questions
What is estimated average glucose (eAG)?
eAG translates an A1C percentage into the same units your meter or CGM uses. It comes from the ADAG study formula: eAG in mg/dL = 28.7 × A1C - 46.7. For example, an A1C of 7% corresponds to an eAG of about 154 mg/dL (8.6 mmol/L).
How can I calculate my A1C?
You cannot measure a true A1C at home: it is a laboratory blood test (or a clinic analyzer). What you can do is estimate it from an average glucose with the ADAG formula, A1C = (average mg/dL + 46.7) / 28.7. Enter your 14 to 90 day CGM average above, or use GMI, which is the CGM-specific version of the same idea.
What is my A1C if my average blood sugar is 110?
About 5.5%, from the ADAG line. An average of 126 mg/dL maps to about 6.0%, 140 mg/dL to about 6.5% and 154 mg/dL to about 7.0%. These are estimates from a long-run average: a handful of fingerstick readings does not make a three-month average, and fasting readings usually sit below the true daily mean.
What is a good A1C?
The American Diabetes Association names 7% or less as the recommended target for most people living with diabetes, so a 7.0 sits right at that general goal. The right target is individual and depends on age, overall health and the risk of lows, and the ADA expects the test at least twice a year, more often when treatment changes. Always discuss your personal target with your care team.
What is a normal A1C?
For diagnosis the ADA bands are: below 5.7% normal, 5.7% to 6.4% prediabetes, 6.5% or higher diabetes. Only a laboratory A1C counts for diagnosis; an A1C estimated from average glucose on this page is orientation, never a diagnosis.
Why is my GMI different from my lab A1C?
GMI estimates A1C purely from your CGM average glucose, while a lab A1C also reflects how long your red blood cells live and other individual factors. A gap of a few tenths of a percent is common, and both numbers stay useful: GMI reflects the sensor data you can act on day to day, while the lab value is the clinical reference. Anything that changes red-cell lifespan or the hemoglobin itself shifts a lab A1C without changing your glucose: iron-deficiency anemia can read falsely high, kidney failure or liver disease can distort the result, and hemoglobin variants interfere with some assays (NIDDK).
What is A1C in mmol/mol?
Many countries report A1C in IFCC units (mmol/mol) instead of percent. The conversion is mmol/mol = (A1C% - 2.15) × 10.929, so 7% equals 53 mmol/mol. The calculator on this page shows both at once.
Can I estimate A1C from my CGM data?
Yes, that is exactly what the glucose management indicator (GMI) does: it converts your CGM average glucose into an A1C-style percentage. Keep in mind it is an estimate, not a lab result. Sugar Sense shows your average glucose and time in range for the same periods, so you always have the underlying numbers too.
Can this calculator replace a lab A1C test?
No. It converts and estimates. Diagnosis and treatment decisions rest on the laboratory test; use this page to understand the number, not to replace it.
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This tool is for education only. It is not medical advice, it does not replace laboratory testing, and it must never be used for insulin dosing or other treatment decisions. Always work with your healthcare team. See our full medical disclaimer.
