A1C of 10.5% is an average glucose of 255 mg/dL

Estimated average glucose at A1C 10.5%

255 mg/dL

In mmol/L: 14.2 mmol/L
A1C entered: 10.5%
ADA range: the range the ADA uses to diagnose diabetes

An A1C of 10.5% corresponds to an estimated average glucose of 255 mg/dL, or 14.2 mmol/L, across roughly the previous two to three months. In IFCC units that A1C is about 91 mmol/mol.

The ADA uses this range diagnostically. One practical note: for values this high the conversion is extrapolating well beyond where most of the study data sat, so treat the estimated average as an order of magnitude rather than a precise figure.

The scale is gentler than it looks. Moving from here to 10.6% shifts the estimated average by only about 3 mg/dL, to roughly 258 mg/dL — well inside the 0.5-point band the assay is allowed to wander within.

Ancestry-linked haemoglobin variants can interfere with certain assay methods specifically, which is a reason a result that looks inconsistent with everything else is worth raising rather than accepting.

Two numbers can be identical and describe quite different weeks. That is not a flaw in the measurement so much as a limit of what any average can say.

A1C looks back over roughly the previous two to three months, because it tracks glycation in red blood cells and those cells circulate for about 120 days before being replaced.

Laboratory methods differ from one another, so comparing a result from one lab against a result from another introduces a spread that has nothing to do with your glucose. Same-lab comparisons are the cleanest kind.

Convert a different A1C value

A1C to estimated average glucose, 10.0% to 11.0%
A1C	eAG (mg/dL)	eAG (mmol/L)
10.0%	240 mg/dL	13.3 mmol/L
10.1%	243 mg/dL	13.5 mmol/L
10.2%	246 mg/dL	13.7 mmol/L
10.3%	249 mg/dL	13.8 mmol/L
10.4%	252 mg/dL	14 mmol/L
10.5%	255 mg/dL	14.2 mmol/L
10.6%	258 mg/dL	14.3 mmol/L
10.7%	260 mg/dL	14.4 mmol/L
10.8%	263 mg/dL	14.6 mmol/L
10.9%	266 mg/dL	14.8 mmol/L
11.0%	269 mg/dL	14.9 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

10.5% A1C is what in average glucose?

Around 255 mg/dL — 14.2 mmol/L if your readings use that scale. The conversion for 10.5% comes from the ADAG study regression published in 2008.

Where does 10.5% fall on the ADA scale?

The ADA describes 10.5% 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.

Would a different lab report the same 10.5%?

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.

Is 10.5% 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.

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