A1C of 5.9% is an average glucose of 123 mg/dL

Estimated average glucose at A1C 5.9%

123 mg/dL

In mmol/L: 6.8 mmol/L
A1C entered: 5.9%
ADA range: the range the ADA defines as prediabetes

At 5.9%, the estimated average glucose works out to 123 mg/dL (6.8 mmol/L). If your report uses IFCC units instead of a percentage, the equivalent is around 41 mmol/mol.

This is in the ADA prediabetes band. Two different sample types — a venous laboratory draw versus a point-of-care fingerstick — can also land a few tenths apart on the same day in the same person.

A1C 5.9% sits in the lower half of the ADA prediabetes band. People often want to know how far it is from 6.5%: six tenths, which in estimated-average terms is about 17 mg/dL of glucose.

The scale is gentler than it looks. Moving from here to 6.0% shifts the estimated average by only about 3 mg/dL, to roughly 126 mg/dL — well inside the 0.5-point band the assay is allowed to wander within.

The equation was fitted across 507 people. It describes that group well; it describes any one member of it only approximately, which is precisely why the word "estimated" is in the name.

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.

Convert a different A1C value

A1C to estimated average glucose, 5.4% to 6.4%
A1C	eAG (mg/dL)	eAG (mmol/L)
5.4%	108 mg/dL	6 mmol/L
5.5%	111 mg/dL	6.2 mmol/L
5.6%	114 mg/dL	6.3 mmol/L
5.7%	117 mg/dL	6.5 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

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 5.9% convert to in mg/dL?

An A1C of 5.9% works out to an estimated average glucose of 123 mg/dL, or 6.8 mmol/L, using the ADA equation eAG = 28.7 x A1C - 46.7 published by Nathan and colleagues in Diabetes Care in 2008.

Which range does the ADA place 5.9% in?

The ADA describes 5.9% 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.

Is 5.9% the same in mmol/mol?

Some countries report A1C in IFCC units rather than NGSP percent. 5.9% is approximately 41 mmol/mol, so a report from the UK, Australia or much of Europe may show that number instead.

What time period does an A1C of 5.9% 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.

Get a quarterly nudge to re-check your numbers

Four emails a year: a reminder to re-take your numbers, and what changed in the guidance behind these tools. No spam, unsubscribe any time.

Double opt-in: you will get one confirmation email and nothing else until you click it.