How do you convert HbA1c to average glucose?

The ADAG study formula estimates average glucose (eAG) from HbA1c as eAG (mg/dL) = 28.7 × A1c − 46.7, or eAG (mmol/L) = 1.59 × A1c − 2.59. For example, an HbA1c of 7% corresponds to an eAG of about 154 mg/dL (8.6 mmol/L).

What is GMI and how is it different from HbA1c?

The Glucose Management Indicator (GMI) estimates a lab-like A1c from the mean glucose measured by a CGM, using GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL). GMI reflects recent CGM data, while HbA1c is a blood test averaging roughly the prior 3 months; the two can differ for an individual.

Calculator · glucose metrics

HbA1c to Average Glucose (eAG) & GMI Calculator

Free tool · Updated July 2026

Convert an HbA1c into an estimated average glucose (eAG), and convert a CGM mean glucose into a Glucose Management Indicator (GMI), using the standard clinical formulas.

HbA1c → estimated average glucose (eAG)

Your HbA1c (%)

eAG (mg/dL)

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eAG (mmol/L)

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Formula (ADAG study): eAG mg/dL = 28.7 × A1c − 46.7; eAG mmol/L = 1.59 × A1c − 2.59.

CGM mean glucose → GMI

Mean glucose

Units

GMI (estimated A1c)

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Formula (Bergenstal et al., 2018): GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL).

Illustrative and educational only. These are population-level estimates, not diagnoses. An individual's eAG or GMI can differ from a laboratory HbA1c because of red-blood-cell turnover, anemia, pregnancy, kidney disease, and other factors. Do not change medication based on this tool. Discuss your results with a qualified clinician.

How these numbers relate

HbA1c is a blood test that reflects your average glucose over roughly the previous two to three months. eAG simply expresses that same HbA1c on the everyday glucose scale (mg/dL or mmol/L) so it is easier to compare with a meter or CGM reading. GMI is different: it estimates a lab-like A1c from the mean glucose your CGM measured, usually over 14 days or more. Because GMI and HbA1c come from different sources, the two can disagree for a given person — a gap that itself can be clinically useful. For more, see HbA1c vs CGM and GMI vs HbA1c.

See the shape behind the number

A single average hides the spikes and crashes that a continuous trace reveals. See what your curve says.

Check your glucose

Sources

Nathan DM, et al. Translating the A1C assay into estimated average glucose values (ADAG study), Diabetes Care, 2008.
Bergenstal RM, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from CGM, Diabetes Care, 2018.
American Diabetes Association — Understanding A1C.

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