Formula
Average glucose (mg/dL) = 28.7 × HbA1c − 46.7
Average glucose (mmol/L) = average glucose (mg/dL) ÷ 18
This formula comes from the international ADAG study, which compared HbA1c with thousands of glucose readings.
HbA1c chart
| HbA1c | Average glucose | Meaning |
|---|---|---|
| 5.0% | 97 mg/dL (5.4 mmol/L) | Normal |
| 5.7% | 117 mg/dL (6.5 mmol/L) | Start of prediabetes range |
| 6.5% | 140 mg/dL (7.8 mmol/L) | Diabetes range |
| 7.0% | 154 mg/dL (8.6 mmol/L) | Common treatment target |
| 8.0% | 183 mg/dL (10.2 mmol/L) | Above target |
| 9.0% | 212 mg/dL (11.8 mmol/L) | High |
| 10.0% | 240 mg/dL (13.4 mmol/L) | Very high |
What the ranges mean
| HbA1c | Category (ADA) |
|---|---|
| Below 5.7% | Normal |
| 5.7% – 6.4% | Prediabetes |
| 6.5% or higher | Diabetes (confirmed by a repeat test) |
Frequently asked questions
What is a normal HbA1c?
Below 5.7%. Between 5.7% and 6.4% is prediabetes and 6.5% or more is in the diabetes range.
What HbA1c should people with diabetes aim for?
Many adults with diabetes aim for below 7%, but your doctor will set a personal target.
How often should I test HbA1c?
People with diabetes usually test every 3–6 months. Others at risk may test once a year.
Sources
- Nathan DM, et al. Translating the A1C assay into estimated average glucose values (ADAG study). Diabetes Care, 2008. Link
- American Diabetes Association. Diagnosis of diabetes. Link
Medical disclaimer: This calculator gives estimates for general information only. It is not a diagnosis or a substitute for advice from a doctor or registered dietitian. Please consult a healthcare professional before making changes to your diet, exercise or medicines, especially if you are pregnant, have a medical condition or take regular medication.
Last updated: 20 October 2026. Read our editorial policy.
