A1C Calculator – HbA1c to Average Glucose (eAG)

Convert an HbA1c result into estimated average glucose (eAG) in mg/dL and mmol/L, or estimate A1C from an average glucose value. The calculator uses the equation from the A1C-Derived Average Glucose (ADAG) study.

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Medical disclaimer: This calculator is intended for educational and informational purposes and does not replace professional medical advice, diagnosis, laboratory interpretation, or treatment. Laboratory methods and reference intervals vary. Always consult a qualified healthcare professional about your results.

How the A1C Calculator works

The A1C (HbA1c) test measures the percentage of hemoglobin that has glucose attached. Because red blood cells live for about three months, A1C reflects average blood glucose over roughly the previous 2–3 months.

Estimated average glucose (eAG) translates the A1C percentage into the same units people see on a glucose meter (mg/dL or mmol/L). The relationship was defined by the international ADAG study, which compared A1C with continuous and frequent fingerstick glucose readings.

Two directions

  • A1C → eAG: enter an A1C percentage to see the matching average glucose.
  • Average glucose → A1C: enter an average glucose (mg/dL or mmol/L) to see the A1C it would correspond to.

Formula used

eAG (mg/dL) = 28.7 × A1C (%) − 46.7
eAG (mmol/L) = eAG (mg/dL) ÷ 18
Estimated A1C (%) = (average glucose mg/dL + 46.7) ÷ 28.7

Glucose in mmol/L is multiplied by 18 to convert to mg/dL before the reverse calculation.

Worked example

  • A1C 7.0% → eAG = 28.7 × 7.0 − 46.7 = 154 mg/dL (154.2 ÷ 18 ≈ 8.6 mmol/L)
  • Average glucose 126 mg/dL → A1C = (126 + 46.7) ÷ 28.7 ≈ 6.0%

Interpreting the result

The American Diabetes Association uses these A1C ranges (laboratory-measured, NGSP-certified methods):

A1CADA categoryApprox. eAG
Below 5.7%Normal< 117 mg/dL
5.7–6.4%Prediabetes117–137 mg/dL
6.5% or higherDiabetes threshold≥ 140 mg/dL

A diagnosis is made by a clinician — usually confirmed with repeat testing — not from a calculated value. Individual A1C targets are set together with a healthcare professional.

Limitations

  • The calculated value is an estimate and does not replace a laboratory HbA1c measurement.
  • Anemia, recent blood loss or transfusion, hemoglobin variants (e.g. sickle cell trait), pregnancy, kidney disease and some medications can make A1C less representative of average glucose.
  • Two people with the same A1C can have different average glucose levels; the ADAG equation describes a population-level relationship.
  • Average glucose from a meter or CGM depends on when and how often readings are taken.

Frequently asked questions

Estimated average glucose (eAG) expresses an A1C result in mg/dL or mmol/L — the same units as a glucose meter — using the ADAG study equation.

eAG (mg/dL) = 28.7 × A1C − 46.7. Divide by 18 to get mmol/L. For example, an A1C of 7% corresponds to about 154 mg/dL (8.6 mmol/L).

Only approximately. Red blood cell lifespan, hemoglobin variants and how glucose was sampled all affect the relationship, so the estimated A1C can differ from a measured A1C.

Conditions affecting red blood cells (anemia, blood loss, transfusion), hemoglobin variants, kidney disease, pregnancy and lab method differences can all cause a measured A1C to differ from what average glucose predicts.

They are related but not identical. GMI is calculated from CGM data using a different equation; this calculator uses the ADAG eAG equation.
Medical disclaimer: This calculator is intended for educational and informational purposes and does not replace professional medical advice, diagnosis, laboratory interpretation, or treatment. Laboratory methods and reference intervals vary. Always consult a qualified healthcare professional about your results.