A1C calculator
Convert an A1C result to estimated average glucose, or estimate A1C from an average glucose reading in mg/dL or mmol/L.
Convert A1C and average glucose
Choose the result you have. A1C accepts 4 to 14%. For glucose, choose the unit shown by your meter or report.
Your estimate
Enter a value and select Calculate to see its conversion, calculation steps, and A1C category.
This estimate is not a diagnosis. A clinician interprets laboratory results and usually confirms a diagnosis with repeat testing. Learn what an A1C test measures.
Get urgent help for warning signs. A very high glucose reading with vomiting, confusion, or trouble breathing needs prompt medical care. Low glucose with confusion, fainting, or a seizure also needs prompt care. Do not use this calculator to decide whether symptoms are urgent.
How this A1C calculator works
This A1C calculator uses the relationship reported by Nathan and colleagues in the A1C-Derived Average Glucose study. The study compared A1C with average glucose collected over about three months, using continuous glucose monitoring and frequent fingerstick readings. Its equation is eAG (mg/dL) = 28.7 × A1C (%) − 46.7.1 We convert between glucose units using 18.016: mmol/L = mg/dL ÷ 18.016. To estimate A1C from glucose, the calculator reverses the equation: A1C (%) = (average glucose in mg/dL + 46.7) ÷ 28.7. The displayed steps show the value before rounding; the final glucose is rounded to a whole mg/dL and one decimal mmol/L, and A1C to one decimal place.
How to read the result
The category shown uses ADA diagnostic cut points for A1C: below 5.7% is the normal range, 5.7% to 6.4% is the prediabetes range, and 6.5% or higher is the diabetes range.2 These labels describe ranges used in clinical screening and diagnosis. The calculator cannot diagnose you. A glucose-derived A1C is an estimate, and a single test result does not establish a diagnosis. A clinician considers the actual test, your health context, and whether repeat testing is needed. If a result is near a cut point, discuss the laboratory result with a clinician rather than treating a rounded estimate as definitive.
For example, an A1C of 6.5% produces an estimated average of about 140 mg/dL (7.8 mmol/L). That does not mean that every glucose reading was near 140. Two people with the same average can have different patterns during the day. Likewise, entering a glucose average yields a mathematically corresponding A1C estimate, not the result of a laboratory test. Keep the original units and source beside the converted figure when you share it, so a clinician can tell whether it came from a lab, a meter, or a CGM summary.
What eAG can and cannot tell you
Estimated average glucose is a way to express an A1C-derived average in familiar glucose units. The ADAG relationship came from a study population and is a statistical estimate, not a conversion that makes the two tests interchangeable for every person. Averages also hide highs, lows, and daily swings. A meter reading is a snapshot; eAG is a longer-term estimate associated with A1C. Use the number as a conversation aid, not as a treatment target or a reason to change medication. For more context, see our A1C chart and guide to A1C versus glucose.
The ADAG study's relationship was built from repeated glucose measurements alongside A1C in hundreds of participants, rather than from a single spot reading.1 That makes it useful for translating a population-level relationship into an understandable estimate, while leaving room for individual differences. If the conversion seems surprising, first check that the units were entered correctly and that the average covers the period you think it does. Then bring both the original readings and the estimated value to a clinician. The calculation itself cannot explain why two measures differ.
A1C to eAG chart
These rounded values use the same ADAG equation. They are estimates, not individual predictions.1
| A1C | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5% | 97 | 5.4 |
| 6% | 126 | 7.0 |
| 7% | 154 | 8.5 |
| 8% | 183 | 10.2 |
| 9% | 212 | 11.8 |
| 10% | 240 | 13.3 |
| 11% | 269 | 14.9 |
| 12% | 298 | 16.5 |
A1C, eAG, and GMI are different measures
Glucose management indicator (GMI) is a number calculated from average glucose measured by a continuous glucose monitor (CGM). It may resemble an A1C percentage, but it is derived from CGM data and can differ from a laboratory A1C.3 This page estimates eAG from A1C or estimates A1C from an entered average glucose; it does not calculate GMI. Bring your CGM summary and laboratory results to your clinician if the numbers do not seem to agree.
Questions people ask
Can this A1C calculator diagnose diabetes?
No. It performs a mathematical conversion and labels a screening range. Diagnosis requires clinician review of appropriate tests and usually confirmation with repeat testing.2
Why might my meter average and eAG differ?
They can come from different time windows, sampling patterns, and measurement methods. The ADAG equation is an estimate based on study averages, so your own readings may not line up exactly.1
How do I convert mmol/L to mg/dL?
For this tool, multiply mmol/L by 18.016 to get mg/dL. It then reverses the ADAG equation to estimate A1C.
Is GMI the same as A1C?
No. GMI is calculated from CGM glucose data. A1C is a laboratory measurement; the two can differ, so ask a clinician how to interpret your own results.
What should I bring to an appointment?
Bring the laboratory report with its date, your glucose log or CGM summary, and a list of questions. Note whether a glucose average includes overnight and after-meal readings, since that helps explain what the average represents.
Useful questions include: Which result should guide my follow-up? Should this test be repeated? Does my glucose record cover enough days to compare with the lab result? Is there a reason the tests might not agree in my situation? The ADA standards discuss diagnostic pathways and confirmation, while the ADAG paper describes the population relationship behind eAG.2, 1 Your care team can put the result in context with your history and other findings. You do not need to solve the discrepancy on your own.
Sources: Nathan et al., “Translating the A1C assay into estimated average glucose values,” Diabetes Care, 2008 (PMID 18540046); American Diabetes Association, “Diagnosis and Classification of Diabetes: Standards of Care in Diabetes, 2025” (PMID 39651986); Bergenstal et al., “Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring,” Diabetes Care, 2018 (PMID 30224348).
This page is general information, not medical advice. A high result, new symptoms, or a mismatch between tests is a reason to contact a clinician. Our supplement comparison guide is separate from diagnosis and care.