HbA1c and average glucose
HbA1c is the share of haemoglobin with glucose attached — a picture of average blood sugar over the past two to three months. The ADAG study links it to average glucose:
eAG (mg/dL) = 28.7 × HbA1c − 46.7 · eAG (mmol/L) = 1.59 × HbA1c − 2.59
| HbA1c | mmol/mol | Avg glucose | Range |
|---|---|---|---|
| 5.0% | 31 | 97 mg/dL · 5.4 mmol/L | Normal |
| 5.7% | 39 | 117 mg/dL · 6.5 mmol/L | Prediabetes from here |
| 6.5% | 48 | 140 mg/dL · 7.8 mmol/L | Diabetes from here |
| 7.0% | 53 | 154 mg/dL · 8.6 mmol/L | Common treatment target |
| 8.0% | 64 | 183 mg/dL · 10.1 mmol/L |
Common questions
What formula converts HbA1c to average glucose?
The ADAG study's linear formula: average glucose (mg/dL) = 28.7 × HbA1c% − 46.7. It's a population-level average relationship, so any one person's actual average can differ from what their HbA1c predicts.
Is this the same as a home glucose meter reading?
No — a meter reading is your blood sugar at that instant; HbA1c reflects an average over roughly the past 2–3 months (how long red blood cells last), so the two numbers answer different questions and shouldn't be expected to match a same-day reading.
For general information only — not medical advice. Talk to a doctor about anything that concerns you.