A1C of 6.4% is an average glucose of 137 mg/dL

Estimated average glucose at A1C 6.4%

137 mg/dL

In mmol/L: 7.6 mmol/L
A1C entered: 6.4%
ADA range: the range the ADA defines as prediabetes

At 6.4%, the estimated average glucose works out to 137 mg/dL (7.6 mmol/L). If your report uses IFCC units instead of a percentage, the equivalent is around 46 mmol/mol.

Inside the ADA prediabetes range. It helps to know what the assay can resolve: NGSP certification permits about half a percentage point of variation, so movement smaller than that is not really movement.

A1C 6.4% is the top of the ADA prediabetes range, one tenth below its diabetes threshold. This is the value where reading a single result in isolation is least useful and where a repeat test genuinely changes the picture.

Step up one tenth and the estimate moves by around 3 mg/dL: 6.5% gives about 140 mg/dL. Since a certified assay may itself vary by roughly 0.5 percentage points, a single tenth of movement between two tests is not really movement.

The estimated average is a summary of a summary: your A1C summarises months, and the conversion summarises the relationship between A1C and glucose across a whole study population.

This is a single frame from a moving picture. A1C summarises a period, so one value locates you on the scale while telling you nothing about which direction you were travelling.

Certification sets how far a method may sit from the reference standard, which is not the same as a confidence interval for one person on one day. The practical upshot is the same: small differences deserve a shrug.

One question that reliably produces a useful answer: is there anything about me that makes this particular test harder to interpret? Your clinician can answer that; a calculator cannot.

Convert a different A1C value

A1C to estimated average glucose, 5.9% to 6.9%
A1C	eAG (mg/dL)	eAG (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
6.9%	151 mg/dL	8.4 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

How much average glucose is an A1C of 6.4%?

An estimated average glucose near 137 mg/dL, or 7.6 mmol/L. This applies the ADA-published conversion to an A1C of 6.4%, and describes roughly the last three months.

Which ADA category does an A1C of 6.4% belong to?

The ADA describes 6.4% 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.

What time period does an A1C of 6.4% describe?

Roughly the previous two to three months of glucose exposure, weighted towards the most recent weeks, because A1C tracks glycation across the lifespan of red blood cells.

Is 6.4% the same in mmol/mol?

Some countries report A1C in IFCC units rather than NGSP percent. 6.4% is approximately 46 mmol/mol, so a report from the UK, Australia or much of Europe may show that number instead.

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