How do I convert A1c to average blood sugar?
The formula
eAG (mg/dL) = (28.7 × A1c) − 46.7
For mmol/L, divide the result by 18. Or convert directly with eAG (mmol/L) = (1.59 × A1c) − 2.59.
The full table
| A1c | mg/dL | mmol/L | Category |
|---|---|---|---|
| 5.0% | 97 | 5.4 | Normal |
| 5.5% | 111 | 6.2 | 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 adult target |
| 7.5% | 169 | 9.4 | Above target |
| 8.0% | 183 | 10.2 | Above target |
| 9.0% | 212 | 11.8 | Well above target |
| 10.0% | 240 | 13.4 | High complication risk |
| 11.0% | 269 | 14.9 | Very high risk |
| 12.0% | 298 | 16.5 | Very high risk |
Why your meter average may not match
It is common for the eAG from an A1c and the average on your meter to disagree, sometimes by a lot. Usually the meter is the misleading one, for a simple reason: you do not test at random.
Most people test when fasting, before meals, or when they suspect something is wrong. That systematically under-samples the post-meal peaks, which pulls the meter average below the true 24-hour average. A continuous glucose monitor, which samples every few minutes, usually agrees with A1c far more closely.
There are also biological reasons for a mismatch. Some people glycate hemoglobin faster or slower than average for the same glucose exposure — described as a high or low "glycation gap". And in anemia, recent blood loss, kidney disease, pregnancy or sickle cell trait, the A1c itself becomes unreliable.
What the conversion cannot tell you
eAG is an average, and an average hides variability. A steady 154 mg/dL and a sawtooth between 60 and 250 both give an A1c around 7%. The second carries more risk and feels considerably worse.
If your A1c looks acceptable but you feel unstable, that gap is worth raising — it is a good reason to ask about continuous monitoring, which reports time in range rather than a single number.
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