HbA1c to Blood Glucose Converter

What Is HbA1c?

HbA1c (glycated hemoglobin) measures the percentage of hemoglobin molecules in your blood that have glucose attached to them.
Red blood cells live about 120 days, and the most recent month carries about half the weight, so the figure reflects your average blood sugar over roughly the past 2 to 3 months rather than the past few hours.
That is why it survives the morning of nervous good behaviour before a blood test, and a single fasting glucose reading does not.

ADA 2008 Formula

The American Diabetes Association (ADA) published the eAG (estimated Average Glucose) formula in 2008, derived from the ADAG clinical study:

Average Glucose (mg/dL) = (HbA1c × 28.7) − 46.7
Average Glucose (mmol/L) = Average Glucose (mg/dL) ÷ 18.0156

Reverse Calculation

HbA1c (%) = (Average Glucose mg/dL + 46.7) ÷ 28.7

This is the direction most calculators leave out, and it is the one continuous glucose monitor users ask about: the app reports a 14-day average in mg/dL or mmol/L, and the question is what A1c that corresponds to before the next appointment.
Set the direction above to convert either way.

For a sensor average, the GMI is the better answer

Sensor apps already do this sum, with a different formula. The GMI (Glucose Management Indicator, Bergenstal and colleagues, 2018) was fitted on CGM data rather than on the ADAG finger-sticks:

GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)

The two agree near 7%, where 154 mg/dL gives 7.0% either way, and drift apart at the ends. A 100 mg/dL average is 5.1% by the reversed ADAG line and 5.7% by the GMI. The calculator shows both when you convert this direction. Neither will match your lab A1c exactly, and the gap between an estimate and the lab figure can be half a point or more.

Which page do you want?

If you only ever go from A1c to a glucose figure, the A1C to Blood Sugar Calculator does that one job with one box.
If you want to convert a single meter reading between mg/dL and mmol/L, without any A1c involved, use the Blood Glucose Unit Converter.

Diabetes Classification (ADA Standards of Care)

• Normal: HbA1c below 5.7% (avg glucose below 117 mg/dL / 6.5 mmol/L)
• Pre-diabetes: HbA1c 5.7%–6.4% (avg glucose 117–137 mg/dL / 6.5–7.6 mmol/L)
• Diabetes: HbA1c 6.5% or higher (avg glucose 140+ mg/dL / 7.8+ mmol/L)

Treatment Targets

For people already diagnosed with type 2 diabetes, the general ADA treatment target is HbA1c below 7.0% (avg glucose below 154 mg/dL / 8.6 mmol/L). Individual targets may vary.

HbA1c vs Fasting Glucose

A single fasting glucose reading can vary day to day based on recent meals, stress, and illness. HbA1c provides a much longer-term picture. Both tests together give the most complete assessment.

When HbA1c lies

The test counts glucose stuck to hemoglobin over a red blood cell’s lifetime, so anything that changes how long those cells live shifts the result without your blood sugar changing at all.

Reads falsely low when red cells die early: hemolytic anemia, sickle cell disease, recent blood loss or transfusion, later pregnancy, and erythropoietin treatment in kidney disease.

Reads falsely high when red cells live longer than usual: iron deficiency anemia, B12 or folate deficiency, and after a splenectomy.

Iron deficiency belongs in the second list, not the first. It is a common thing to get backwards, and it matters, because an iron-deficient patient can be handed a diabetes diagnosis on a number that iron tablets alone would bring down. If your result surprises you, ask whether a full blood count was done alongside it.