Medical disclaimer: this calculator converts between units using published formulas. It does not diagnose diabetes or replace advice from a doctor. Diagnosis requires laboratory testing confirmed by a healthcare professional.
What is A1C?
The A1C test (also called HbA1c or glycated hemoglobin) measures the percentage of hemoglobin in your red blood cells that has glucose attached. Because red blood cells live about three months, A1C reflects your average blood sugar over the past 2–3 months, weighted toward the most recent weeks. Unlike a finger-stick reading, it doesn't change with what you ate this morning.
A1C to average blood sugar formula
The conversion comes from the A1C-Derived Average Glucose (ADAG) study, which compared A1C with thousands of continuous and finger-stick glucose readings. The American Diabetes Association uses its regression equation:
eAG (mmol/L) = 1.59 × A1C − 2.59
A1C = (eAG mg/dL + 46.7) ÷ 28.7
IFCC (mmol/mol) = (A1C − 2.15) × 10.929
Example: an A1C of 7%.
- eAG = 28.7 × 7 − 46.7 = 154 mg/dL
- In mmol/L: 1.59 × 7 − 2.59 = 8.5 mmol/L
- IFCC units: (7 − 2.15) × 10.929 = 53 mmol/mol
A1C chart
| A1C | eAG (mg/dL) | eAG (mmol/L) | IFCC (mmol/mol) | ADA category |
|---|---|---|---|---|
| 5.0% | 97 | 5.4 | 31 | Normal |
| 5.5% | 111 | 6.2 | 37 | Normal |
| 5.7% | 117 | 6.5 | 39 | Prediabetes |
| 6.0% | 126 | 7.0 | 42 | Prediabetes |
| 6.5% | 140 | 7.7 | 48 | Diabetes range |
| 7.0% | 154 | 8.5 | 53 | Diabetes range |
| 7.5% | 169 | 9.3 | 58 | Diabetes range |
| 8.0% | 183 | 10.1 | 64 | Diabetes range |
| 8.5% | 197 | 10.9 | 69 | Diabetes range |
| 9.0% | 212 | 11.7 | 75 | Diabetes range |
| 9.5% | 226 | 12.5 | 80 | Diabetes range |
| 10.0% | 240 | 13.3 | 86 | Diabetes range |
| 11.0% | 269 | 14.9 | 97 | Diabetes range |
| 12.0% | 298 | 16.5 | 108 | Diabetes range |
| 13.0% | 326 | 18.1 | 119 | Diabetes range |
| 14.0% | 355 | 19.7 | 130 | Diabetes range |
What do A1C numbers mean?
| A1C | Category (ADA) |
|---|---|
| Below 5.7% | Normal |
| 5.7% – 6.4% | Prediabetes (increased risk of type 2 diabetes) |
| 6.5% or higher | Diabetes (confirmed with a repeat test) |
For many non-pregnant adults with diabetes, the ADA suggests an A1C goal below 7%, but targets are individual. A higher goal may be safer for older adults or people prone to low blood sugar; a lower goal may suit others if it can be reached safely. Agree on your personal target with your care team.
GMI: A1C estimated from a CGM
If you use a continuous glucose monitor, your report may show a Glucose Management Indicator (GMI). It estimates the A1C you'd expect from your CGM average over at least 14 days:
GMI and lab A1C often differ by 0.5 points or more, because A1C is also affected by how long your red blood cells live and how readily glucose attaches to hemoglobin. Neither is "wrong" — they measure different things.
When A1C can be misleading
A1C assumes a normal red-blood-cell lifespan. Results can be falsely high or low with:
- Anemia (iron-deficiency anemia can raise A1C; hemolytic anemia and recent blood loss can lower it)
- Hemoglobin variants such as sickle cell trait or HbC
- Chronic kidney disease, advanced liver disease, or recent blood transfusion
- Pregnancy, especially the second and third trimesters
In these situations your provider may rely more on glucose readings, CGM data or other tests such as fructosamine.
How often should A1C be tested?
The ADA generally recommends testing at least twice a year for people with diabetes who are meeting their goals, and quarterly when treatment changes or goals aren't being met. People with prediabetes are usually re-tested every year.
Frequently asked questions
What is a normal A1C?
Below 5.7% is considered normal. 5.7%–6.4% indicates prediabetes, and 6.5% or higher on two tests indicates diabetes.
What average blood sugar is an A1C of 6?
About 126 mg/dL (7.0 mmol/L), using eAG = 28.7 × 6 − 46.7.
What A1C is 150 average blood sugar?
About 6.9% — (150 + 46.7) ÷ 28.7 = 6.85%.
Can I calculate my A1C at home?
You can estimate it from the average of many glucose readings or your CGM (as GMI), but only a lab or approved point-of-care A1C test gives your actual A1C.
How quickly can I lower my A1C?
Because A1C reflects about three months of glucose, changes in diet, activity or medication usually show up clearly after 2–3 months. Talk to your healthcare provider before changing treatment.