A1C to Average Glucose (eAG)

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A1C to Average Glucose (eAG)

Health • A1C ↔ eAG

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How to Use the A1C to Average Glucose (eAG)

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Why Use This A1C to Average Glucose (eAG)

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Understanding the A1C to Average Glucose (eAG)

HbA1c ("A1C") is a blood test that reflects your average blood sugar over the past 2–3 months. The American Diabetes Association ADAG formula converts A1C to an estimated average glucose: eAG (mg/dL) = 28.7 × A1C − 46.7. So an A1C of 7% is about 154 mg/dL (8.6 mmol/L).

This converter shows eAG in both US (mg/dL) and international (mmol/L) units and flags the general category (normal, prediabetes or diabetes range). It is for information and education only — not a diagnosis. Always discuss your results with your clinician.

Formula & Logic

Haemoglobin A1c measures the percentage of haemoglobin that has become glycated, which reflects average blood glucose over roughly the preceding two to three months — the lifespan of a red blood cell. Because patients monitor daily glucose in mg/dL or mmol/L but clinicians track A1c as a percentage, a translation is needed. The ADAG study of 2008 established the linear relationship used here, producing "estimated average glucose". The word estimated is doing real work: individual variation in red cell turnover means two people with identical A1c can have meaningfully different average glucose.

eAG (mg/dL) = (28.7 × A1C) − 46.7eAG (mmol/L) = eAG(mg/dL) ÷ 18.0IFCC (mmol/mol) = (A1C% − 2.15) × 10.929

where:

A1C: glycated haemoglobin as a percentage (NGSP units)
eAG: estimated average glucose over the preceding 2–3 months
IFCC: the mmol/mol unit used in the UK, Europe and Australia

Assumptions: A population-level estimate, not a diagnosis. Anaemia, haemoglobin variants, recent transfusion and pregnancy all distort A1c. Diagnostic thresholds are 5.7% for prediabetes and 6.5% for diabetes; treatment targets are individual and set by a clinician.

Step-by-Step Example: An A1c of 7.2%

Translate a test result into the daily glucose numbers a patient actually sees.

A1c result7.2%

Apply the ADAG equation: (28.7 × 7.2) − 46.7 = 206.64 − 46.7 = 159.9 mg/dL.
Convert to mmol/L: 159.9 ÷ 18.0 = 8.9 mmol/L.
To IFCC units: (7.2 − 2.15) × 10.929 = 55.2 mmol/mol.
Compare with a 6.5% result: (28.7 × 6.5) − 46.7 = 139.8 mg/dL.
And with 8.0%: (28.7 × 8.0) − 46.7 = 182.9 mg/dL.
Note the gradient: each 1% of A1c corresponds to about 28.7 mg/dL of average glucose.

ResultA1c 7.2% ≈ 159.9 mg/dL (8.9 mmol/L, 55 mmol/mol)

The constant 28.7 makes the mental shortcut easy: roughly 29 mg/dL per percentage point. A reduction from 8.0% to 7.2% therefore represents about 23 mg/dL lower average glucose — a clinically meaningful change, and one that daily readings alone would not reliably reveal.