Enter your average glucose to see the A1C it usually goes with and your GMI (glucose management indicator), or enter an A1C to see the average glucose behind it. Everything is worked out in your browser; nothing you type is sent anywhere.
GMI and estimated A1C are not the same thing
Both start from your average glucose, but they come from different studies and answer slightly different questions.
- Estimated A1C comes from the ADAG study, which compared people's lab A1C with their average glucose. Its formula is A1C = (average glucose in mg/dL + 46.7) / 28.7.
- GMI was introduced in 2018 for CGM users, so that the number on a CGM report wouldn't be confused with a lab test. Its formula is GMI (%) = 3.31 + 0.02392 × average glucose in mg/dL, or 3.31 + 0.43056 × average glucose in mmol/L.
For the same average, the two land close to each other, usually within a few tenths of a point.
Why your lab A1C may be different
A1C measures how much sugar has attached to your red blood cells over their lifespan, which is about three months. Anything that changes how long those cells live, or how the test reads them, can move the lab result away from what your glucose readings suggest: anemia, recent blood loss or a transfusion, pregnancy, kidney disease, and some hemoglobin variants among them.
So a gap between your GMI and your lab A1C isn't necessarily a mistake on either side. If it is large or keeps coming back, mention it to your care team; they may rely more on one than the other for you.
Quick reference
| A1C | Estimated average glucose |
|---|---|
| 5% | 97 mg/dL · 5.4 mmol/L |
| 6% | 126 mg/dL · 7.0 mmol/L |
| 7% | 154 mg/dL · 8.6 mmol/L |
| 8% | 183 mg/dL · 10.2 mmol/L |
| 9% | 212 mg/dL · 11.8 mmol/L |
| 10% | 240 mg/dL · 13.3 mmol/L |
| 11% | 269 mg/dL · 14.9 mmol/L |
| 12% | 298 mg/dL · 16.5 mmol/L |
Many adults with diabetes aim for an A1C below 7%, but the right target is individual and is something to set with your care team. For the day-to-day picture behind an A1C, see time in range.
Common questions
How do I calculate A1C from average blood sugar?
With the ADAG formula: A1C = (average glucose in mg/dL + 46.7) / 28.7. An average of 154 mg/dL gives an A1C of about 7%.
What is GMI in diabetes?
The glucose management indicator is an estimate of A1C worked out from at least 14 days of CGM readings, using the formula 3.31 + 0.02392 × average glucose in mg/dL.
What average glucose is an A1C of 7%?
About 154 mg/dL (8.6 mmol/L).
Can this calculator replace a lab A1C test?
No. It is an estimate from averages and can differ from a lab result for the reasons above. Use it to understand your numbers, not to make treatment decisions.
Sources
- Nathan DM, Kuenen J, Borg R, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473–1478.
- Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275–2280.
- American Diabetes Association. Standards of Care in Diabetes, section 6: Glycemic goals and hypoglycemia.