What is an A1C test?
The A1C test, also called HbA1c or glycated hemoglobin, shows the percentage of your hemoglobin that has sugar attached to it. Because red blood cells live for about three months, the result reflects your average blood sugar over roughly that time rather than a single moment.
Doctors use A1C to screen for and monitor diabetes. Your own doctor decides how to interpret your result along with other tests and your health history.
What is estimated average glucose (eAG)?
A1C is a percentage, while home meters report glucose in mg/dL or mmol/L. To bridge the two, a research group (the ADAG study) created a formula that converts A1C to an estimated average glucose, or eAG. It helps people picture what their A1C means in the units they see on a meter.
The eAG is an estimate. It is calculated from a population-based line, so it may not match the average on your own meter exactly.
How to convert A1C manually
- Multiply your A1C by 28.7.
- Subtract 46.7 to get eAG in mg/dL.
- Divide by 18.016 to get mmol/L.
To go backwards, add 46.7 to the glucose in mg/dL and divide by 28.7.
A1C to glucose chart
| A1C | eAG mg/dL | eAG mmol/L |
|---|---|---|
| 5% | 97 | 5.4 |
| 6% | 126 | 7.0 |
| 7% | 154 | 8.6 |
| 8% | 183 | 10.2 |
| 9% | 212 | 11.8 |
| 10% | 240 | 13.4 |
| 11% | 269 | 14.9 |
| 12% | 298 | 16.5 |
The calculator above shows the same table and updates your row's value instantly.
A1C ranges
The American Diabetes Association lists these general A1C ranges for adults: below 5.7% is considered normal, 5.7% to 6.4% is in the prediabetes range, and 6.5% or higher is consistent with diabetes.
These are screening categories, not a diagnosis. A diagnosis normally needs confirmatory testing by a clinician, such as a repeat test or a different blood test. Many adults with diabetes are given an A1C goal under 7%, but goals are individual and can be higher or lower depending on age, health and risk of low blood sugar.
Things that can affect A1C
- Conditions that change red blood cell life, such as anemia, sickle cell trait or recent blood loss, can make A1C read too high or low.
- Pregnancy and kidney disease can also affect accuracy.
- Lab methods differ a little, so compare results from the same lab if you can.
- A1C is an average. It can hide large highs and lows, which is why some people also use glucose meters or CGMs.
How often is A1C checked?
How often depends on your situation. People managing diabetes are often tested a few times a year, while others are screened less often. Your clinician will recommend a schedule for you. Use this calculator only to understand the numbers, and bring questions about your care to your doctor.
A1C vs daily glucose readings
A1C and a finger-stick or sensor reading answer different questions. A meter reading shows glucose at one moment, and it can swing with meals, sleep, stress, illness and exercise. A1C blends about three months into one number, weighting the most recent weeks more heavily. Two people with the same A1C can have very different patterns, one steady and one with big highs and lows.
For that reason, clinicians often look at A1C together with daily readings or continuous glucose monitor data instead of relying on either alone.
Why your A1C might not match your meter average
It is common to find that the eAG from your lab A1C is not the same as the average on your meter. Meters are usually checked at certain times of day, often before meals, so the average can miss highs after eating or overnight. Biology also plays a role: some people naturally glycate hemoglobin faster or slower than average, which shifts A1C relative to glucose. If the two numbers keep disagreeing, mention it to your care team rather than trying to fix it yourself.