Blood glucose to A1C conversion uses the ADAG formula: A1C = (average glucose + 46.7) / 28.7. If your 3-month average blood sugar is 154 mg/dL, your predicted A1C is 7.0 percent. This relationship lets you estimate A1C from CGM data or frequent home readings.
The Official Conversion Formula
The American Diabetes Association uses the ADAG (A1C-Derived Average Glucose) study equations, published by Nathan and colleagues in 2008:
- eAG (mg/dL) = 28.7 x A1C – 46.7
- A1C (%) = (eAG + 46.7) / 28.7
For example, an A1C of 6.0 percent predicts an eAG of 126 mg/dL, and an average glucose of 200 mg/dL predicts an A1C of 8.6 percent.
Full Blood Glucose to A1C Conversion Chart
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5.0 | 97 | 5.4 |
| 5.5 | 111 | 6.2 |
| 6.0 | 126 | 7.0 |
| 6.5 | 140 | 7.8 |
| 7.0 | 154 | 8.6 |
| 7.5 | 169 | 9.4 |
| 8.0 | 183 | 10.2 |
| 8.5 | 197 | 10.9 |
| 9.0 | 212 | 11.8 |
| 9.5 | 226 | 12.6 |
| 10.0 | 240 | 13.4 |
| 11.0 | 269 | 14.9 |
| 12.0 | 298 | 16.5 |
Source: Nathan DM et al., Diabetes Care, 2008.
Worked Example: Converting Home Readings to A1C
Imagine you log the following fasting and post-meal glucose values over two weeks:
- Fasting average: 110 mg/dL
- Post-breakfast (2 hr): 160 mg/dL
- Post-lunch (2 hr): 150 mg/dL
- Post-dinner (2 hr): 170 mg/dL
A rough weighted average might fall near 140 mg/dL. Using the ADAG formula: A1C = (140 + 46.7) / 28.7 = 6.5 percent. This is a ballpark estimate; you can read more about A1C ranges and what they mean.
When the Formula Can Be Off
The ADAG equation assumes typical red blood cell turnover. A1C can read falsely high or low in people with:
- Anemia (iron deficiency, B12 deficiency, or chronic disease)
- Hemoglobinopathies such as sickle cell or thalassemia
- Recent blood transfusion or major blood loss
- Pregnancy
- Chronic kidney disease
In these cases, clinicians may use fructosamine (2-3 week average) or CGM-derived Glucose Management Indicator (GMI) instead.
CGM, GMI, and the New Standard
Continuous glucose monitors capture a reading every 1-5 minutes. After 14 or more days of wear, the device calculates a Glucose Management Indicator (GMI). GMI uses a slightly different equation:
GMI (%) = 3.31 + 0.02392 x mean glucose in mg/dL
According to Bergenstal and colleagues, GMI and lab A1C usually agree within 0.3 percentage points. A gap larger than that can signal an individual glycation pattern that makes lab A1C a less reliable marker.
Blood Glucose to A1C: Quick Mental Math
If you want a ballpark without a calculator, remember:
- Average glucose 100 mg/dL roughly equals A1C 5
- Average glucose 150 mg/dL roughly equals A1C 7
- Average glucose 200 mg/dL roughly equals A1C 8.5
- Every 28 mg/dL increase in average glucose adds about 1 percent to A1C
Using the Conversion to Guide Lifestyle Changes
Knowing how your daily numbers translate to A1C can sharpen motivation. If your CGM 14-day average is 170 mg/dL (GMI around 7.5), a 20 mg/dL reduction through diet and walking would bring your predicted A1C closer to 6.8. Explore our diet and nutrition guides for practical steps.
When to Use the Formula vs. Get a Lab
| Situation | Best Tool |
|---|---|
| Routine diagnosis | Lab A1C |
| Between doctor visits | ADAG estimate or CGM GMI |
| Anemia or hemoglobinopathy | Fructosamine or CGM GMI |
| Pregnancy | Fasting and post-meal glucose |
| Post-transfusion | Fructosamine until 3+ months out |
The ADA still treats lab A1C as the diagnostic standard, but these alternatives provide valuable short-term tracking.
The Bottom Line
Converting blood glucose to A1C is straightforward with the ADAG formula – roughly every 28.7 mg/dL change in average glucose equals one percent change in A1C. Use the conversion to translate CGM or home-meter data into a projected A1C and to see how daily habits affect the lab number. Just remember that individual biology varies, so always confirm big decisions with a lab test and a conversation with your clinician.
