Glucose to HbA1c Calculator

This calculator converts between average blood glucose and HbA1c using the equation from the ADAG study. Enter an average glucose to see the estimated HbA1c (in % and mmol/mol), or enter an HbA1c to see the estimated average glucose (in mg/dL and mmol/L). It can help people and clinicians relate the lab’s HbA1c to the glucose numbers they see on a meter or continuous glucose monitor.

How the conversion works

The A1c-Derived Average Glucose (ADAG) study compared HbA1c with average glucose measured over three months, using continuous glucose monitoring plus frequent fingerstick readings, in 507 people with type 1 diabetes, type 2 diabetes and no diabetes. It produced these equations:

• estimated average glucose (mg/dL) = 28.7 × HbA1c (%) − 46.7
• estimated average glucose (mmol/L) = 1.59 × HbA1c (%) − 2.59

To go the other way, the calculator rearranges them: HbA1c = (average glucose + 46.7) ÷ 28.7 for mg/dL, and (average glucose + 2.59) ÷ 1.59 for mmol/L.

HbA1c is also reported in IFCC units (mmol/mol). The calculator converts with the international master equation: NGSP % = 0.09148 × IFCC + 2.152.

HbA1c and estimated average glucose

Calculated from the equations above. Values may differ by a point from other published tables because of rounding.

What the categories mean

• Below 5.7% (39 mmol/mol): below the prediabetes range.
• 5.7% to 6.4% (39–47 mmol/mol): the prediabetes range used by the American Diabetes Association. UK and WHO guidance describes 6.0–6.4% (42–47 mmol/mol) as high risk.
• 6.5% (48 mmol/mol) or above: in the diabetes range. Diagnosis needs a laboratory HbA1c and clinical interpretation.

Limits of the estimate

• It’s an average, not a single reading. One fingerstick or a fasting value can’t be converted, because HbA1c reflects roughly the last three months and is weighted towards recent weeks.
• Individuals vary. The equation describes the population. In any one person the lab HbA1c can differ noticeably from the estimate.
• HbA1c itself can be unreliable with anaemia, haemoglobin variants (such as sickle cell trait), recent bleeding or transfusion, pregnancy, and some kidney and liver conditions.
• Range: the equation was developed for HbA1c of roughly 4–12%. Outside that range the calculator warns you.

Frequently asked questions

What average glucose equals an HbA1c of 7%?

About 154 mg/dL (8.6 mmol/L), using the ADAG equation.

Can I convert a single glucose reading to HbA1c?

No. HbA1c reflects average glucose over about three months, so a single reading can’t be converted. Use an average from a CGM or meter download.

What’s the difference between % and mmol/mol?

They’re two units for the same HbA1c test. Percent is the older NGSP/DCCT unit; mmol/mol is the IFCC unit used in the UK and much of Europe. For example, 6.5% is 48 mmol/mol and 7.0% is 53 mmol/mol.

Why doesn’t my lab HbA1c match the estimate?

The equation is an average relationship. Red cell lifespan, haemoglobin variants, anaemia and how glucose varies through the day can all shift an individual’s HbA1c away from the estimate.

Can this diagnose diabetes?

No. Diagnosis depends on laboratory testing and clinical judgement, and needs confirmation in most situations.

Medical disclaimer

Sources & references

• Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ. “Translating the A1C assay into estimated average glucose values.” Diabetes Care, 2008;31(8):1473–1478. pmc.ncbi.nlm.nih.gov
• NICE. Type 2 diabetes in adults: management (NG28). nice.org.uk/guidance/ng28
• Geistanger A, et al. “Statistical methods for monitoring the relationship between the IFCC reference measurement procedure for HbA1c and the designated comparison methods in the United States, Japan, and Sweden.” Clinical Chemistry, 2008;54:1379–1385.