What this calculator does
HbA1c reflects average blood glucose over roughly the preceding two to three months, but it is reported as a percentage, which does not connect to the readings a glucose meter shows. Estimated average glucose translates it into those familiar units.
The relationship is linear and easy to hold in mind. An A1C of 6 per cent corresponds to about 125 mg/dL, and each additional percentage point adds roughly 29 mg/dL, so 7 per cent is about 154.
The formula
The ADAG study fitted a straight line between A1C and average glucose: multiply the A1C by 28.7 and subtract 46.7 to get mg/dL. Dividing by 18.018 converts to mmol/L.
| Term | Meaning |
|---|---|
| HbA1c | The share of haemoglobin with glucose attached, reflecting the preceding two to three months. |
| eAG | Estimated average glucose: the same information expressed in glucose units. |
| ADAG study | The 2008 trial that established the conversion used here. |
The inputs explained
| Field | What to enter |
|---|---|
| HbA1c (%) | Your HbA1c as a percentage, from a laboratory result. |
When to use it
Making sense of an A1C result
Average glucose is easier to relate to than a percentage, especially alongside meter readings.
Comparing lab and meter data
If your meter average is far from the eAG, it is worth asking your clinician why.
Following a change over time
Seeing the glucose equivalent of a change in A1C makes the size of the shift more tangible.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What glucose level does each A1C represent?
Four A1C values and their estimated average glucose.
| HbA1c | Estimated average glucose | In mmol/L |
|---|---|---|
| 5% | 97 mg/dL | 5.4 mmol/L |
| 6% | 125 mg/dL | 7.0 mmol/L |
| 7% | 154 mg/dL | 8.6 mmol/L |
| 9% | 212 mg/dL | 11.7 mmol/L |
Questions
How accurate is the conversion?
It describes the average relationship found in the ADAG study, but individuals vary around that line. Two people with the same A1C can have genuinely different average glucose levels, so it is an estimate rather than a measurement.
Why might my meter average differ?
Meter readings are not evenly spread across the day, and most people test more before meals than after. Red blood cell lifespan also varies between individuals, which shifts A1C independently of glucose.
When is A1C unreliable?
In anaemia, recent blood loss or transfusion, some haemoglobin variants, pregnancy and kidney disease, among others. Any of these can make A1C misrepresent average glucose, and your clinician will know whether they apply.
What A1C should I be aiming for?
That is a question for the clinician managing your care. Targets differ by individual and depend on age, other conditions, treatment and risk of low blood sugar. There is no single right number.
For cholesterol figures from the same routine bloods, see the LDL cholesterol calculator. For the risk ratio from a lipid panel, see the cholesterol ratio calculator.