This calculator gives general estimates for information only. It does not replace advice from your doctor, pharmacist or another qualified health professional.
Two units for the same number
Blood glucose is reported in milligrams per deciliter (mg/dL) in the United States and in millimoles per liter (mmol/L) in Canada, the UK, Australia and much of Europe; France often uses grams per liter (g/L). A meter bought abroad or a lab report from another country can therefore show a number that looks alarming or reassuring when it is neither. The conversion is simple because glucose has a fixed molecular weight of about 180 g/mol:
- mmol/L = mg/dL ÷ 18
- mg/dL = mmol/L × 18
- g/L = mg/dL ÷ 100
Worked example: a fasting reading of 95 mg/dL
- 95 ÷ 18 = 5.3 mmol/L.
- 95 ÷ 100 = 0.95 g/L.
- For a fasting test, 95 mg/dL is in the normal range of 70 to 99 mg/dL.
Reference ranges (American Diabetes Association)
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose | 70–99 mg/dL (3.9–5.5 mmol/L) | 100–125 mg/dL (5.6–6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or more |
| 2 hours after a glucose drink | below 140 mg/dL (7.8 mmol/L) | 140–199 mg/dL | 200 mg/dL (11.1 mmol/L) or more |
| A1C | below 5.7% | 5.7%–6.4% | 6.5% or more |
A diagnosis is never made on a single home reading: it needs lab tests, usually repeated. Below 70 mg/dL (3.9 mmol/L) is low blood sugar; the usual first aid is the “15-15 rule”: 15 g of fast sugar, then a new check after 15 minutes.
From A1C to average glucose
The A1C test measures the share of hemoglobin carrying glucose, which reflects your average blood sugar over the past two to three months. The ADAG study linked the two with eAG (mg/dL) = 28.7 × A1C − 46.7. Labs outside the US often report A1C in IFCC units: mmol/mol = (A1C − 2.15) × 10.929.
| A1C | Average glucose | IFCC |
|---|---|---|
| 5% | 97 mg/dL (5.4 mmol/L) | 31 mmol/mol |
| 5.7% | 117 mg/dL (6.5 mmol/L) | 39 mmol/mol |
| 6.5% | 140 mg/dL (7.8 mmol/L) | 48 mmol/mol |
| 7% | 154 mg/dL (8.6 mmol/L) | 53 mmol/mol |
| 8% | 183 mg/dL (10.2 mmol/L) | 64 mmol/mol |
| 9% | 212 mg/dL (11.8 mmol/L) | 75 mmol/mol |
With the default A1C of 5.5%, the estimated average is about 111 mg/dL, or 6.2 mmol/L, which is 37 mmol/mol.
Tips for accurate readings
- Wash and dry your hands before a finger-stick test: fruit sugar on the skin can raise the result.
- “Fasting” means at least 8 hours without food or caloric drinks.
- Home meters and continuous monitors can differ from lab results by 10 to 15%.
- A1C can be misleading with anemia, recent blood loss, kidney disease or some hemoglobin variants.