A1C of 6.6% is an average glucose of 143 mg/dL

Estimated average glucose at A1C 6.6%

143 mg/dL

In mmol/L: 7.9 mmol/L
A1C entered: 6.6%
ADA range: the range the ADA uses to diagnose diabetes

The estimated average glucose behind an A1C of 6.6% is 143 mg/dL, or 7.9 mmol/L. That A1C would appear as approximately 49 mmol/mol on a report using IFCC units.

At this level the ADA diagnostic criteria apply. The most useful thing this page offers is the translation into an average glucose, which is often easier to hold onto than a percentage — and a reason to bring the printed report to an appointment rather than a screenshot.

For comparison, 6.7% comes out at approximately 146 mg/dL, about 3 mg/dL higher. Differences of a tenth sit under the roughly 0.5-point measurement tolerance, so neighbouring values are often indistinguishable in practice.

Which glucose unit you see is a matter of geography: the United States and India generally report mg/dL, while the UK, Australia and Canada generally report mmol/L.

Anything that alters red blood cell turnover — anaemia, recent blood loss, a transfusion, pregnancy, chronic kidney disease, some haemoglobin variants — moves A1C independently of glucose, in either direction.

A steady day and a volatile day can average out to the same figure. If that distinction matters for you, it is continuous monitoring rather than a periodic average that shows it.

Anything that happened in the last fortnight is already influencing this figure, while something from four months ago has largely aged out of it.

Convert a different A1C value

A1C to estimated average glucose, 6.1% to 7.1%
A1C	eAG (mg/dL)	eAG (mmol/L)
6.1%	128 mg/dL	7.1 mmol/L
6.2%	131 mg/dL	7.3 mmol/L
6.3%	134 mg/dL	7.4 mmol/L
6.4%	137 mg/dL	7.6 mmol/L
6.5%	140 mg/dL	7.8 mmol/L
6.6%	143 mg/dL	7.9 mmol/L
6.7%	146 mg/dL	8.1 mmol/L
6.8%	148 mg/dL	8.2 mmol/L
6.9%	151 mg/dL	8.4 mmol/L
7.0%	154 mg/dL	8.5 mmol/L
7.1%	157 mg/dL	8.7 mmol/L

Computed with eAG (mg/dL) = 28.7 x A1C - 46.7 (Nathan 2008). mmol/L is derived from mg/dL using the glucose factor 18.0182.

Estimated average glucose (ADAG / Nathan) — eAG (mg/dL) = 28.7 x A1C - 46.7. Verified 2026-07-30 against Nathan et al., Diabetes Care 2008 (ADAG study) (A population regression: in the ADAG study, individuals at the same A1C had meaningfully different mean glucose. The A1C assay itself carries about +/- 0.5 percentage points under NGSP certification.)

Official sources

Nathan DM et al., Translating the A1C Assay Into Estimated Average Glucose Values, Diabetes Care 2008 — The ADAG study that produced the eAG equation used on this page.
American Diabetes Association — Standards of Care in Diabetes — Where the A1C ranges quoted here are defined.
NGSP — A1C assay standardisation and certification criteria — Why two lab results half a point apart can mean nothing changed.

Frequently asked questions

What does 6.6% convert to in mg/dL?

An A1C of 6.6% works out to an estimated average glucose of 143 mg/dL, or 7.9 mmol/L, using the ADA equation eAG = 28.7 x A1C - 46.7 published by Nathan and colleagues in Diabetes Care in 2008.

Does 6.6% count as prediabetes or diabetes?

The ADA describes 6.6% as the range the ADA uses to diagnose diabetes. That is a definition of a numeric range rather than a diagnosis: the ADA asks clinicians to confirm results with a repeat test and to read them alongside your history.

Is 6.6% a target?

This page converts a number rather than recommending one. Glycemic targets are individualised by a clinician according to your diagnosis, your other results and your risk of hypoglycaemia.

Would a different lab report the same 6.6%?

Not necessarily. Analytical methods vary between laboratories, and a point-of-care fingerstick can read differently from a venous draw, so comparisons are cleanest within one lab.

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