A1C of 13% is an average glucose of 326 mg/dL

Estimated average glucose at A1C 13%

326 mg/dL

In mmol/L: 18.1 mmol/L
A1C entered: 13.0%
ADA range: the range the ADA uses to diagnose diabetes

An A1C of 13.0% corresponds to an estimated average glucose of 326 mg/dL, or 18.1 mmol/L, across roughly the previous two to three months. In IFCC units that A1C is about 119 mmol/mol.

This is within the range the ADA uses to diagnose diabetes. The conversion below tells you what average glucose it corresponds to. It does not tell you what to do, and it cannot see the rest of your chart.

Step up one tenth and the estimate moves by around 3 mg/dL: 13.1% gives about 329 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.

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.

Bringing the printed report to an appointment beats bringing a screenshot of a calculator, because your clinician can read it against everything else in your chart.

Convert a different A1C value

A1C to estimated average glucose, 12.5% to 13.5%
A1C	eAG (mg/dL)	eAG (mmol/L)
12.5%	312 mg/dL	17.3 mmol/L
12.6%	315 mg/dL	17.5 mmol/L
12.7%	318 mg/dL	17.6 mmol/L
12.8%	321 mg/dL	17.8 mmol/L
12.9%	324 mg/dL	18 mmol/L
13.0%	326 mg/dL	18.1 mmol/L
13.1%	329 mg/dL	18.3 mmol/L
13.2%	332 mg/dL	18.4 mmol/L
13.3%	335 mg/dL	18.6 mmol/L
13.4%	338 mg/dL	18.8 mmol/L
13.5%	341 mg/dL	18.9 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

What is an A1C of 13.0% in average blood sugar?

Roughly 326 mg/dL (18.1 mmol/L). The figure comes from the ADAG regression, eAG = 28.7 x A1C - 46.7, applied to an A1C of 13.0%.

Does 13.0% count as prediabetes or diabetes?

The ADA describes 13.0% 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 13.0% 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 13.0%?

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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