What this calculator does
An A1C test (also called HbA1c) shows your average blood sugar over about the past three months. It's reported as a percentage, while a home meter or CGM shows glucose in mg/dL or mmol/L. Estimated average glucose (eAG) turns your A1C into those same units, so you can compare it with the numbers you see every day. You can also go the other way: enter an average glucose and see the A1C it matches.
How it's calculated
The American Diabetes Association uses the equation from the A1C-Derived Average Glucose (ADAG) study, which compared A1C with frequent glucose readings in 507 people with and without diabetes:
A1C = (eAG in mg/dL + 46.7) ÷ 28.7
eAG (mmol/L) = eAG (mg/dL) ÷ 18
Calcist converts mg/dL to mmol/L by dividing by 18, which reproduces the ADA's published table to one decimal.
Worked example
An A1C of 7%: 28.7 × 7 = 200.9, and 200.9 − 46.7 = 154.2, so the eAG is about 154 mg/dL. In mmol/L that's 154.2 ÷ 18 = 8.6 mmol/L. Going back, a 14-day CGM average of 183 mg/dL gives (183 + 46.7) ÷ 28.7 = 8.0%.
A1C to eAG chart
| A1C | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5.0% | 97 | 5.4 |
| 5.5% | 111 | 6.2 |
| 6.0% | 125 | 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 | 11.0 |
| 9.0% | 212 | 11.8 |
| 9.5% | 226 | 12.6 |
| 10.0% | 240 | 13.4 |
| 10.5% | 255 | 14.1 |
| 11.0% | 269 | 14.9 |
| 11.5% | 283 | 15.7 |
| 12.0% | 298 | 16.5 |
A1C result ranges
The CDC lists these ranges for the A1C test. They describe the A1C number itself, not the eAG.
| A1C | CDC range |
|---|---|
| Below 5.7% | Normal |
| 5.7% to 6.4% | Prediabetes |
| 6.5% or above | Diabetes |
Only a health care provider can diagnose diabetes. They decide what a result means for you, and they often look at more than one test.
When the estimate can be off
- It's an average across many people. Two people with the same A1C can have different real averages. The ADAG equation describes the overall relationship, not your personal one.
- Some conditions change A1C itself. The CDC lists severe anemia, kidney failure, liver disease, blood disorders such as sickle cell anemia or thalassemia, some medicines, blood loss or transfusions, and early or late pregnancy.
- An average hides swings. The same eAG can come from steady readings or from highs and lows. A meter or CGM shows the pattern.
- Very high or low values are further from the study data, so treat them as rough.
This is an estimate to help you read your results. Talk to your doctor about your own numbers and targets.
Sources
- American Diabetes Association: eAG/A1C conversion calculator and table
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ, for the ADAG Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31(8):1473.
- CDC: A1C test for diabetes and prediabetes — the result ranges and conditions that can make A1C misleading.