Related health guide
A1C vs. average blood sugar: why the numbers differ — practical context and examples to help you use this calculator.
How to use the A1C calculator
Find the A1C percentage on your laboratory report and enter the number without the percent sign. For example, enter 6.5 for an A1C of 6.5%. The calculator shows both commonly used glucose units together, so you can compare the estimate with the units used by your care team.
This version accepts A1C values from 4% to 15%. That is an input limit for the tool, not a healthy range or a statement that every value within it has the same predictive accuracy. If your report falls outside the range, ask your clinician to interpret it. A report in mmol/mol uses a different A1C scale and cannot be entered directly.
A1C to eAG formula
The A1C-Derived Average Glucose (ADAG) relationship used by the American Diabetes Association is:
eAG (mg/dL) = 28.7 × A1C (%) − 46.7.
We convert the unrounded mg/dL result to mmol/L by dividing by 18, the conventional approximate glucose conversion factor. Results are displayed as whole mg/dL and one decimal place in mmol/L. The two displays may not convert exactly into each other because each is rounded separately.
This equation estimates an average from A1C. It does not reconstruct a series of glucose readings or reveal how often glucose was high or low.
Worked example: A1C of 7%
For an A1C of 7%, the calculation is 28.7 × 7 − 46.7 = 154.2 mg/dL. The displayed results are 154 mg/dL and 8.6 mmol/L. This is a worked arithmetic example, not a recommended treatment target.
If a glucose meter reading differs from this number, that alone does not mean the calculator or meter is wrong: a single reading and a longer-term average describe different things.
A1C conversion chart
These examples use the same equation and rounding as the calculator. The rows are reference conversions, not diagnostic categories.
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 4 | 68 | 3.8 |
| 5 | 97 | 5.4 |
| 5.7 | 117 | 6.5 |
| 6 | 126 | 7.0 |
| 6.5 | 140 | 7.8 |
| 7 | 154 | 8.6 |
| 8 | 183 | 10.2 |
| 9 | 212 | 11.8 |
| 10 | 240 | 13.4 |
| 11 | 269 | 14.9 |
| 12 | 298 | 16.5 |
| 13 | 326 | 18.1 |
| 14 | 355 | 19.7 |
| 15 | 384 | 21.3 |
A1C versus fasting blood glucose
A1C reflects glucose exposure over roughly the preceding three months. Fasting glucose measures glucose at a particular time after fasting. An eAG conversion is therefore not a fasting-glucose prediction, and fasting-glucose diagnostic cutoffs should not be applied to this output.
Our HOMA-IR calculator uses fasting glucose and fasting insulin for a different calculation. Do not substitute this eAG result for a measured fasting glucose value in that tool.
When the estimate may be less reliable
A1C interpretation can be affected by changes in red blood cells, some forms of anemia, recent blood loss or transfusion, certain hemoglobin variants, and some kidney or liver conditions. Pregnancy can also change how the test is used. The relevance depends on the condition and laboratory method.
If A1C and your glucose records do not agree, discuss the discrepancy with your healthcare team rather than adjusting treatment from this conversion. The calculator cannot account for these individual factors or determine which test is appropriate.
Frequently asked questions
Can I calculate A1C from one blood sugar reading?
No. A single glucose reading is not an average. This tool takes a measured A1C percentage and estimates average glucose in one direction only.
Is this the same as the average on my glucose monitor?
Not necessarily. This estimate comes from an A1C-based population relationship. A monitor average comes from the readings collected during its reporting period, which may cover different dates.
Does an average show glucose spikes and lows?
No. Different patterns can produce the same average. This page does not replace review of actual glucose readings.
Does the result tell me how much insulin to take?
No. It is not a dose calculator and does not set individual treatment goals.
Sources
- American Diabetes Association: Estimated average glucose — ADAG equation and reference conversions.
- NIDDK: The A1C Test & Diabetes — test meaning and limitations.
Sources checked October 15, 2026. PureCalc independently implements the equation; the organizations cited do not endorse this calculator.