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A1C and average blood glucose are two ways of describing the same thing — your typical blood sugar over the past two to three months. A1C is a percentage; estimated average glucose (eAG) is in the mg/dL or mmol/L units of a everyday glucose meter. This calculator converts between them.
It is for information and understanding only, and is not a diagnosis or a substitute for testing and medical advice.
How is it calculated?
The conversion
The tool uses the regression from the ADAG study, which related lab A1C to directly measured average glucose:
eAG (mg/dL) = 28.7 × A1C − 46.7
and, rearranged, A1C (%) = (eAG + 46.7) ÷ 28.7. To get mmol/L, divide mg/dL by 18.0182.
A rough reference
| A1C | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5% | 97 | 5.4 |
| 6% | 126 | 7.0 |
| 7% | 154 | 8.6 |
| 8% | 183 | 10.2 |
What it means, and doesn’t
A1C reflects an average, so it can hide swings — highs and lows that cancel out still average to a middling number. The eAG conversion is a population estimate; an individual’s meter average can differ from their lab A1C for reasons like red-blood-cell lifespan. Use these figures to understand the relationship, and rely on your clinician and lab tests for any decisions.
Worked example
An A1C of 7% converts to an estimated average glucose of 28.7 × 7 − 46.7 = 154.2 mg/dL, which is about 8.6 mmol/L. Going the other way, if a meter reports an average of 126 mg/dL, that corresponds to an A1C of (126 + 46.7) ÷ 28.7 ≈ 6.0%.
FAQ
How do I convert A1C to average glucose?+
Multiply the A1C by 28.7 and subtract 46.7 to get eAG in mg/dL: an A1C of 7% is 28.7 × 7 − 46.7 = 154 mg/dL. Divide mg/dL by 18.0182 for mmol/L. The calculator does both.
What is eAG?+
Estimated average glucose — your A1C expressed in the same units as a home glucose meter (mg/dL or mmol/L). It makes A1C easier to relate to day-to-day readings, since both describe average blood sugar.
Why doesn’t my meter average match my A1C?+
The eAG formula is a population average, and individuals vary — factors such as red-blood-cell lifespan can shift the relationship. Meters also sample only when you test, missing overnight and between-meal values. Some difference is normal; discuss significant gaps with your clinician.
What A1C is considered normal?+
General reference ranges put normal below 5.7%, prediabetes at 5.7–6.4%, and diabetes at 6.5% or above — but interpretation is individual and belongs with your healthcare provider. This tool converts units; it does not diagnose.
Can A1C hide blood sugar swings?+
Yes. Because it’s an average over months, frequent highs and lows can cancel out to a moderate A1C. That’s why A1C is often looked at alongside time-in-range and daily readings rather than on its own.