A1C of 6.3% is an average glucose of 134 mg/dL

Estimated average glucose at A1C 6.3%

134 mg/dL

In mmol/L: 7.4 mmol/L
A1C entered: 6.3%
ADA range: the range the ADA defines as prediabetes

Putting 6.3% through the ADA equation gives an estimated average glucose of 134 mg/dL — the same figure expressed as 7.4 mmol/L. Laboratories reporting in IFCC units would print that A1C as roughly 45 mmol/mol.

The ADA calls 5.7% to 6.4% prediabetes. A value here is worth a conversation about repeat testing and about what your other numbers, particularly fasting glucose, are showing alongside it.

A1C 6.3% sits close under the 6.5% diagnostic line. The conversion is exact arithmetic on the reported value, while the reported value itself carries the usual laboratory tolerance. Both facts are worth taking to an appointment.

Each additional tenth of a percentage point adds about 3 mg/dL to the estimated average, so 6.4% works out to roughly 137 mg/dL. That step is smaller than the 0.5-point tolerance NGSP allows on the assay, which is worth holding in mind before reading much into a one-tenth difference.

Because the measurement covers a rolling window of months, retesting much sooner than three months largely re-measures the same period and adds little information.

The precision of the reported figure invites more confidence than it deserves. A result printed to one decimal place still carries the method tolerance around it, so treat the last digit as approximate.

Writing the value and its date somewhere you will find it again is worth more than reading another page about it, because the comparison is the part that carries information.

Moving country, or moving between health systems, can change the units on your reports without anything changing in your blood. Worth checking before comparing an old result to a new one.

Convert a different A1C value

A1C to estimated average glucose, 5.8% to 6.8%
A1C	eAG (mg/dL)	eAG (mmol/L)
5.8%	120 mg/dL	6.7 mmol/L
5.9%	123 mg/dL	6.8 mmol/L
6.0%	126 mg/dL	7 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

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

6.3% A1C is what in average glucose?

Around 134 mg/dL — 7.4 mmol/L if your readings use that scale. The conversion for 6.3% comes from the ADAG study regression published in 2008.

What does the ADA say about 6.3%?

The ADA describes 6.3% as the range the ADA defines as prediabetes. 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.

Does an A1C of 6.3% tell me about my glucose swings?

No. It is an average, and averages hide shape. Two people with this same A1C can have very different daily ranges; continuous monitoring is what shows that pattern.

Can something other than glucose produce an A1C of 6.3%?

Yes. Anaemia, recent blood loss, transfusion, pregnancy, chronic kidney disease and some haemoglobin variants all shift A1C independently of glucose, in either direction.

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