About the A1C Calculator
The A1C (HbA1c) test measures the percentage of haemoglobin in your red blood cells that has glucose attached. Because red blood cells live for about three months, it reflects your average blood sugar over roughly the previous 8–12 weeks. This calculator converts that percentage into estimated average glucose (eAG) — the same units you see on a glucose meter — in both mg/dL and mmol/L.
It also works in reverse: enter an average glucose from a meter or continuous glucose monitor and get the A1C it corresponds to. The result shows the IFCC value in mmol/mol used on lab reports in the UK, Europe and Australia, and where the A1C falls against the standard normal, prediabetes and diabetes thresholds.
The conversion uses the ADAG study equation adopted by the American Diabetes Association. It describes averages across many people; your own A1C can read higher or lower than your meter average because of anaemia, kidney disease, haemoglobin variants or recent blood loss. Diagnosis always requires lab testing.
With the default inputs, the estimated average glucose is 154 mg/dL. Change any value above to recalculate instantly.
How to use the a1c calculator
- 1Choose whether you are converting from A1C or from average glucose.
- 2Enter your A1C percentage from a lab report, or your average glucose.
- 3If converting from glucose, pick mg/dL or mmol/L.
- 4Read the estimated average glucose, A1C and IFCC value.
- 5Check which range the A1C falls in and use the chart for other values.
Formula and method
The eAG equation comes from the A1C-Derived Average Glucose (ADAG) study, which compared lab A1C results with thousands of glucose readings from continuous monitors and finger-sticks over three months. The linear fit it produced is the one used by the American Diabetes Association. Rearranging it converts an average glucose back to an A1C.
mg/dL values are converted to mmol/L by dividing by 18.016 (from glucose’s molar mass of 180.16 g/mol). The IFCC value uses the NGSP–IFCC master equation, which relates the US-style percentage to the international reference unit reported in many countries.
- A1C
- Glycated haemoglobin, % (NGSP/DCCT units)
- eAG
- Estimated average glucose, mg/dL
- IFCC
- HbA1c in mmol per mol of haemoglobin
Worked examples
A1C of 7%
28.7 × 7 − 46.7 = 154.2 mg/dL, which is 154.2 ÷ 18.016 ≈ 8.6 mmol/L. In IFCC units, (7 − 2.15) × 10.929 ≈ 53 mmol/mol. 7% is a common treatment target for adults with diabetes.
A1C of 5.9%
28.7 × 5.9 − 46.7 = 122.6 mg/dL (about 6.8 mmol/L). An A1C between 5.7% and 6.4% is in the prediabetes range, where lifestyle changes can substantially lower the risk of type 2 diabetes.
CGM average of 9.0 mmol/L to A1C
9.0 mmol/L × 18.016 = 162.1 mg/dL. (162.1 + 46.7) ÷ 28.7 ≈ 7.3%, or about 56 mmol/mol in IFCC units.
Frequently asked questions
What is a normal A1C level?+
For people without diabetes, an A1C below 5.7% is considered normal. 5.7% to 6.4% indicates prediabetes, and 6.5% or higher on two separate tests is one of the criteria used to diagnose diabetes.
What A1C should I aim for if I have diabetes?+
The American Diabetes Association suggests below 7% for many non-pregnant adults, but targets are individualised — tighter for some younger people, looser (for example under 8%) for older adults or those prone to hypoglycaemia. Agree your target with your clinician.
Why does my meter average not match my A1C?+
Finger-stick averages depend on when you test and miss overnight and post-meal peaks. A1C can also be affected by red blood cell lifespan, anaemia, kidney disease, pregnancy and haemoglobin variants, so some people consistently read higher or lower than their true average.
How do I convert A1C percent to mmol/mol?+
Use the IFCC equation: mmol/mol = (A1C% − 2.15) × 10.929. For example, 6.5% is (6.5 − 2.15) × 10.929 ≈ 48 mmol/mol, the diagnostic threshold used in the UK.
How often should A1C be checked?+
People with diabetes who are meeting their goals are usually tested about twice a year, and every three months when treatment changes or targets are not being met, because A1C reflects roughly the last three months.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.