HbA1c ⇄ Average Glucose (eAG) Converter

Understanding the HbA1c to average glucose converter — concept and principle

HbA1c (glycated haemoglobin) shows the share of haemoglobin with glucose attached and reflects average blood glucose over roughly the past two to three months. This converter translates HbA1c in percent (NGSP units) into estimated average glucose (eAG) in mg/dL and mmol/L, converts it to IFCC units (mmol/mol), and shows the American Diabetes Association category.

One A1c value, three ways to write it: 6.5% ≈ 140 mg/dL ≈ 7.76 mmol/L ≈ 48 mmol/mol.

How it is calculated

eAG (mg/dL) = 28.7 × HbA1c − 46.7
eAG (mmol/L) = eAG (mg/dL) ÷ 18.016
IFCC (mmol/mol) = (HbA1c − 2.15) × 10.929
Category: below 5.7% normal, 5.7–6.4% prediabetes range, 6.5% or more diabetes range

The principle

Glucose in the blood binds slowly and irreversibly to haemoglobin inside red blood cells, which live about 120 days. The higher the average glucose, the more haemoglobin becomes glycated, so HbA1c works as a long-term average weighted towards recent weeks. The ADAG study (Nathan et al., 2008) measured glucose frequently with continuous monitors and finger-sticks in over 500 people and found a near-linear relationship, which gave the 28.7 and 46.7 constants. The IFCC formula converts between the US NGSP percentage and the international reference method, which measures glycated haemoglobin more specifically and reports it in mmol/mol.

Worked example

Input: HbA1c = 6.5%.
eAG = 28.7 × 6.5 − 46.7 = 186.55 − 46.7 = 139.85, shown as 140 mg/dL.
In mmol/L: 139.85 ÷ 18.016 = 7.76 mmol/L.
IFCC: (6.5 − 2.15) × 10.929 = 4.35 × 10.929 = 47.54, shown as 48 mmol/mol.
Because 6.5% meets the threshold, the category is diabetes range.

Each point is the calculator re-run with only “HbA1c (%)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

HbA1c (%)	Average glucose (mg/dL)
1.62	0
3.25	47
4.88	93
6.5	140
8.12	186
9.75	233
13	326

How to read the result

Where does your result fall?

For orientation, 6% corresponds to about 126 mg/dL, 7% to about 154 mg/dL and 8% to about 183 mg/dL. Many adults with diabetes are advised to aim for below 7%, though targets are individualised. A diagnosis of diabetes normally needs a repeat abnormal test unless symptoms are clear, so one result at 6.5% is a reason to see a doctor rather than a confirmed diagnosis.

Common mistakes

Treating eAG as your typical finger-stick value; daily glucose swings can be large even when the average is fine.
Using HbA1c when red blood cell lifespan is altered, as in anaemia, recent blood loss or transfusion, pregnancy or some haemoglobin variants.
Mixing up % and mmol/mol units when reading foreign lab reports.

Keep in mind: The eAG equation describes an average relationship, and individuals with the same HbA1c can have mean glucose differing by several tens of mg/dL. This is not a diagnosis; talk to a doctor about your results.

Frequently asked questions

How quickly can HbA1c change?

It reflects about three months, but recent weeks count most, so a meaningful change is usually seen after 2–3 months.

What is 48 mmol/mol in percent?

It equals about 6.5%, the diabetes threshold in both unit systems.

Is HbA1c the same as time in range from a CGM?

No. Time in range shows how many hours glucose stayed within a target band, which HbA1c cannot reveal.

Sources: Nathan DM et al. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31(8):1473–1478. · American Diabetes Association. Standards of Care in Diabetes (Classification and Diagnosis of Diabetes).

Checked 8 Nov 2026. Nathan et al., Diabetes Care 2008 (ADAG); ADA Standards of Care.

Your numbers