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A1C ⇆ Estimated Average Glucose Calculator
Convert HbA1c (%) to estimated average glucose (eAG) using the ADAG study formula — or go the other way, from average glucose to estimated A1C.
Enter HbA1c
Estimates average blood glucose over the preceding ~2–3 months.
%
Estimated Average Glucose
– mg/dL
–
Normal
Prediabetes
Diabetes range
Formula estimate (ADAG study). Individual correlation between A1C and average glucose can vary.
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) |
|---|
Formula
eAG (mg/dL) = 28.7 × A1C − 46.7
eAG (mmol/L) = 1.59 × A1C − 2.59
About this conversion
The eAG formula comes from the ADAG (A1c-Derived Average Glucose) study, which correlated HbA1c with continuous glucose monitoring and frequent self-monitoring data across a large cohort. It lets lab results be reported in the same mg/dL or mmol/L units patients already use for home glucose readings.
Diagnostic categories (ADA)
- Normal: A1C < 5.7%
- Prediabetes: A1C 5.7–6.4%
- Diabetes: A1C ≥ 6.5% (confirmed on repeat testing, or with classic symptoms/random glucose ≥200 mg/dL)
For people with an existing diabetes diagnosis, an individualized target (commonly <7% for many adults, though ranges vary by age and comorbidities) is typically set by the treating clinician rather than the general diagnostic cutoffs above.
Limitations
- Any condition altering red blood cell lifespan (hemolytic anemia, recent transfusion, blood loss, iron deficiency) can make A1C an unreliable estimate of average glucose
- Hemoglobin variants/hemoglobinopathies (e.g. HbS, HbC) may interfere with certain A1C assay methods
- Chronic kidney disease and pregnancy also alter the A1C–glucose relationship
- eAG reflects an average — it does not capture glycemic variability, hypoglycemic episodes, or day-to-day swings
Enter average glucose
Use a mean glucose value (e.g. from CGM data or repeated fasting/random checks).
Estimated A1C
– %
–
Normal
Prediabetes
Diabetes range
This is a reverse estimate of the ADAG formula — a true A1C requires a laboratory blood test.
In mg/dL
–
Entered average glucose
In mmol/L
–
Entered average glucose
Formula
A1C (%) = (Average Glucose[mg/dL] + 46.7) ÷ 28.7
When to use this direction
This reverse calculation is useful for translating a patient's home glucose monitoring average, or a CGM-reported "Glucose Management Indicator," into an approximate A1C for discussion — it is an estimate, not a diagnostic substitute for a laboratory HbA1c assay.
Note on accuracy
The ADAG correlation was derived from population averages, so an individual's true A1C can differ meaningfully from the estimate — particularly with irregular monitoring, non-representative testing times, or any of the red-blood-cell-related limitations noted in the A1C → eAG tab.
