This A1C calculator converts between your A1C percentage and estimated average glucose (eAG) in both directions, so you can turn a lab A1C into an everyday mg/dL number or translate your meter’s average blood sugar to A1C. It also shows the mmol/L equivalent and where your result falls on the American Diabetes Association (ADA) scale.
A1C reflects the percentage of hemoglobin coated with sugar and mirrors your average blood glucose over the prior two to three months. Because red blood cells live about 90 days, A1C smooths out daily spikes and dips into one long-term number that clinicians use to screen for and manage diabetes.
The A1C to Glucose Formula (eAG)
The conversion uses the ADAG study regression the ADA adopted for its A1C-to-eAG tool:
- Average glucose (mg/dL) = 28.7 × A1C − 46.7
- A1C (%) = (average glucose + 46.7) ÷ 28.7
To get mmol/L, divide mg/dL by 18. So an A1C of 7% works out to 28.7 × 7 − 46.7 = 154 mg/dL, or about 8.6 mmol/L. This is what an eAG calculator does: it maps the lab percentage onto the same units your glucose meter shows, making the number easier to relate to daily readings. Remember it is an estimate — a best-fit average, not a guarantee that every reading sat at that level.
What Is a Good A1C? ADA Thresholds
The ADA defines diagnostic bands for adults:
- Normal: below 5.7% (eAG under about 117 mg/dL)
- Prediabetes: 5.7% to 6.4% (eAG roughly 117–137 mg/dL)
- Diabetes: 6.5% or higher (eAG about 140 mg/dL or more)
For many adults already diagnosed with diabetes, a common treatment target is below 7%, though providers individualize goals — some aim tighter, others looser depending on age, hypoglycemia risk, and other conditions. Converting average glucose to A1C helps you sanity-check where months of meter or CGM readings would place you before your next lab draw.
Example: Average Glucose of 154 mg/dL
Suppose your meter reports a two-month average of 154 mg/dL and you want the estimated A1C.
- A1C = (154 + 46.7) ÷ 28.7 = 200.7 ÷ 28.7 = 7.0%
- In mmol/L: 154 ÷ 18 = 8.6 mmol/L
A 7.0% A1C sits in the diabetes range (6.5% and above) and equals the common 7% management target. Going the other way, if a lab returns an A1C of 6.0%, the eAG is 28.7 × 6 − 46.7 = 126 mg/dL — squarely in the prediabetes band and a signal to review diet, activity, and follow-up testing with a provider.
Frequently Asked Questions
What is a good A1C?
Below 5.7% is considered normal by the ADA, 5.7%–6.4% is prediabetes, and 6.5% or higher indicates diabetes. Many adults with diabetes aim for under 7%, but targets are individualized by a healthcare provider based on age, other conditions, and hypoglycemia risk.
How do you convert A1C to average blood glucose?
Multiply your A1C by 28.7 and subtract 46.7 to get estimated average glucose (eAG) in mg/dL. For example, an A1C of 7% equals 28.7 × 7 − 46.7 = 154 mg/dL, or about 8.6 mmol/L when you divide by 18.
How do you convert average blood sugar to A1C?
Add 46.7 to your average glucose in mg/dL, then divide by 28.7. An average of 126 mg/dL gives (126 + 46.7) ÷ 28.7 = 6.0%. This estimate assumes your readings are representative of the whole day over the past two to three months.
What does A1C actually measure?
A1C measures the percentage of hemoglobin in your red blood cells that has glucose attached. Because red blood cells last about three months, A1C reflects your average blood sugar over roughly 90 days rather than a single moment, making it useful for long-term diabetes screening and management.
Why is my eAG different from my meter average?
eAG is a population-based estimate from a regression formula, so it can differ from your own meter or CGM average. Factors like anemia, recent blood loss, pregnancy, kidney disease, and certain hemoglobin variants can also skew A1C. Use both numbers together and discuss discrepancies with your provider.