HbA1c to Average Blood Sugar Converter
Convert between HbA1c and estimated average glucose, in mg/dL or mmol/L, with the diagnostic bands.
HbA1c reflects your average blood glucose over roughly the previous two to three months, because glucose sticks to haemoglobin for the life of a red blood cell. This converts it to an estimated average glucose — the number a glucose meter would show — and back again.
How this is worked out
The conversion is the ADAG study regression: estimated average glucose in mg/dL = 28.7 × HbA1c − 46.7. The IFCC value in mmol/mol, used on lab reports in much of Europe, is (HbA1c% − 2.15) × 10.929.
The ADA diagnostic bands are: below 5.7% normal, 5.7–6.4% prediabetes, and 6.5% or above consistent with diabetes on two separate tests. Most adults with diabetes are given a target below 7%, though targets are individualised — tighter for some younger people, looser where hypoglycaemia is a risk or life expectancy is limited.
HbA1c can mislead. Anaemia, recent blood loss or transfusion, pregnancy, chronic kidney or liver disease, and haemoglobin variants such as sickle cell trait — not rare in parts of India and Africa — all shift the result. Some people also glycate haemoglobin faster or slower than average, so two people with identical average glucose can differ by half a percentage point.
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Common questions
What HbA1c means diabetes?
6.5% or above on two separate tests, or once alongside classic symptoms and a high random glucose. 5.7 to 6.4% is prediabetes — a warning worth acting on, not a diagnosis.
How quickly does HbA1c respond to change?
The most recent month counts for about half the result, so meaningful movement shows within four to six weeks. Retesting sooner than three months rarely tells you anything new.