This A1C calculator converts between hemoglobin A1C (the three-month percentage) and estimated average glucose (eAG) in both mg/dL and mmol/L — the translation between the lab report and the daily numbers on a meter.
The Formula and Its Source
eAG (mg/dL) = 28.7 × A1C − 46.7 — the regression from the international A1C-Derived Average Glucose (ADAG) study, which paired laboratory A1Cs with thousands of meter/CGM readings. A1C measures the share of hemoglobin that glucose has permanently tagged over red cells' ~3-month life, weighted toward the most recent weeks — so it tracks average glucose without being a simple average of anything you'd log. Single readings live on the Blood Sugar Converter. Part of our Health Calculators collection.
The Conversion Table Worth Knowing
| A1C | eAG (mg/dL) | eAG (mmol/L) | Band |
|---|---|---|---|
| 5.0% | 97 | 5.4 | Normal |
| 5.7% | 117 | 6.5 | Prediabetes begins |
| 6.0% | 126 | 7.0 | Prediabetes |
| 6.5% | 140 | 7.8 | Diabetes threshold |
| 7.0% | 154 | 8.6 | Common treatment target |
| 8.0% | 183 | 10.2 | Above target for most |
| 9.0% | 212 | 11.8 | High |
| 10.0% | 240 | 13.3 | High |
Each 1% of A1C is about 29 mg/dL of average glucose — the slope that makes "down 0.5%" a concrete ~14 mg/dL of everyday improvement.
Worked Example (Verified)
- A1C 7.0% → eAG = 28.7 × 7 − 46.7 = 154 mg/dL (8.6 mmol/L)
- CGM average of 140 mg/dL → implied A1C = (140 + 46.7) ÷ 28.7 = 6.5%
- The gap people discover: meter averages often run lower than eAG because fingers get tested at flattering times (fasting, pre-meal) — A1C counts the post-meal peaks you didn't measure
When A1C Misleads
- Anything changing red-cell lifespan skews it: anemia, recent transfusion, blood loss, pregnancy, some kidney conditions — glucose reads fine while A1C lies in either direction.
- The formula is a population regression: two people at 154 mg/dL average can legitimately test 6.7% and 7.3%.
- It weights recent weeks more heavily — a strict month before the test moves A1C, but only partly; it is not a grade on last week.
Related Tools
- Blood Sugar Converter — individual readings, both units
- GFR Calculator — kidney function, the frequent companion test
- Health Calculators — the full collection
Frequently Asked Questions
What is a normal A1C?
Below 5.7% is normal; 5.7–6.4% is prediabetes; 6.5% or higher meets the diabetes criterion (with confirmatory testing as guidelines specify). Many adults with diabetes aim for under 7% — an eAG of about 154 mg/dL.
How do I convert A1C to average blood sugar?
eAG = 28.7 × A1C − 46.7 (mg/dL). A1C 7% → 154 mg/dL; 8% → 183; 6% → 126. Divide by 18 for mmol/L, as the table shows.
Why doesn't my meter average match my A1C?
Three usual reasons: meters sample convenient times and miss peaks; the A1C-glucose relationship varies between individuals; and conditions affecting red blood cells distort A1C itself. CGM time-in-range statistics exist precisely to bridge this gap.
How often should A1C be tested?
Guidelines (ADA) suggest at least twice a year when stable and at goal, quarterly when therapy changes or targets aren't met — your clinician sets the actual cadence.
Can I lower A1C by 1% quickly?
"Quickly" is bounded by red-cell turnover: meaningful change registers in 4–6 weeks, with full reflection at ~3 months. A true 1% drop equals ~29 mg/dL off your average — achievable, and not a one-week project.
Is this A1C calculator free?
Yes — free and instant, for information; your clinician interprets your results in context.