What is estimated average glucose?

Estimated average glucose (eAG) translates an HbA1c into the average blood glucose it corresponds to over the preceding two to three months. It gives patients a number in the same units as their day-to-day meter readings.

What formula does the tool use?

It uses the ADAG study regression: eAG in mg/dL equals 28.7 times the HbA1c percent minus 46.7. The mmol/L value is the mg/dL result divided by 18.018. These are the equations adopted for reporting A1c-derived average glucose.

How do NGSP percent and IFCC mmol/mol relate?

They are two scales for the same measurement. NGSP percent equals the IFCC mmol/mol value divided by 10.929 plus 2.15. For example 53 mmol/mol corresponds to about 7.0 percent.

When is eAG unreliable?

HbA1c reflects red-cell glucose exposure over the cell's lifespan, so anything that shortens or alters that lifespan distorts it. Anaemia, haemoglobinopathies, recent transfusion, pregnancy, and kidney disease can all make eAG misleading.

Why does eAG sometimes differ from my meter average?

eAG is a population regression, so an individual's true average can sit above or below it. It also weights recent glucose more heavily. Use it as a guide for discussion, not an exact match to a meter or sensor average.

What is the HbA1c to Average Glucose Converter (eAG)?

Convert HbA1c between NGSP percent and IFCC mmol/mol and compute estimated average glucose with the ADAG regression formula. A browser-based diabetes calculator for diabetologists, GPs, and diabetes educators that runs entirely on your device. It runs free in your browser on Gera Tools, with nothing uploaded.

HbA1c to Average Glucose Converter (eAG)

Name: HbA1c to Average Glucose Converter (eAG)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Reporting an HbA1c as an estimated average glucose helps patients relate a lab percentage to the glucose numbers they see on a meter or sensor. This converter moves between the NGSP percent and IFCC mmol/mol scales and applies the ADAG regression to give an average glucose in both common units, all in your browser.

How it works

The tool first puts your HbA1c onto the NGSP percent scale, then applies the ADAG study regression:

NGSP%        = IFCC_mmol_per_mol / 10.929 + 2.15
eAG (mg/dL)  = 28.7 × HbA1c% − 46.7
eAG (mmol/L) = eAG_mgdl / 18.018

The same relationships run in reverse to report the IFCC value alongside the percent. The regression is the one adopted internationally for translating A1c into an average glucose.

Common HbA1c values and their eAG equivalents

This table shows representative conversions using the ADAG formula to illustrate the relationship at a glance. All values are illustrative examples only — use the calculator for precise conversions:

HbA1c (%)	HbA1c (mmol/mol)	eAG (mg/dL)	eAG (mmol/L)
5.0	31	97	5.4
6.0	42	126	7.0
6.5	48	140	7.8
7.0	53	154	8.6
7.5	58	169	9.4
8.0	64	183	10.2
9.0	75	212	11.8
10.0	86	240	13.3

The key practical takeaway is that each one-percentage-point rise in HbA1c corresponds to roughly 28 to 29 mg/dL (about 1.6 mmol/L) increase in estimated average glucose.

NGSP versus IFCC: which unit does your lab report?

Lab reports in the United States almost universally use NGSP percent (the familiar 4–14% range). Labs in the United Kingdom, Australia, and most of Europe now report in IFCC mmol/mol following the 2009 international harmonization. A result of 53 mmol/mol (IFCC) equals 7.0% (NGSP) — so the same patient result looks very different on paper depending on where the test was run.

Always note the unit before entering a value, especially when reviewing results from an international source or comparing across different healthcare systems.

When eAG diverges from meter or sensor averages

The ADAG regression gives a population average — an individual’s true mean glucose may sit meaningfully above or below the calculated eAG. Several factors distort HbA1c in ways that make the eAG unreliable:

Haemoglobin variants (sickle cell trait, HbC, HbE) alter red-cell glycation independently of glucose levels.
Anaemia or haemolysis shortens red cell lifespan, lowering HbA1c without a true improvement in glucose control.
Pregnancy increases red-cell turnover, pushing HbA1c downward even at the same average glucose.
Recent transfusion introduces donor cells that dilute glycated haemoglobin.
Iron deficiency anaemia tends to raise HbA1c artificially.

In these situations, fructosamine or continuous glucose monitoring time-in-range data are more reliable guides to actual glycaemic control.

Clinical use

eAG is most useful in diabetes education — helping a patient understand that their 7.2% HbA1c reflects blood sugar averaging around 160 mg/dL (8.9 mmol/L) between tests, rather than just a percentage on a form. It bridges the lab result and the everyday experience of glucose monitoring. This tool is for educational and clinical reference; all patient care decisions should involve a qualified clinician.