The Blood Glucose Unit Converter switches a blood-sugar reading between the two unit systems used worldwide: mg/dL (milligrams per decilitre, used in the US, Germany, France, and Japan) and mmol/L (millimoles per litre, used in the UK, Canada, Australia, and most of Europe). The molecule is identical — only the way it is reported changes.
How it works
Glucose has a molar mass of about 180.16 g/mol. Converting a mass concentration (mg/dL) to a molar concentration (mmol/L) uses this constant:
mmol/L = mg/dL ÷ 18.018
mg/dL = mmol/L × 18.018
The factor 18.018 comes from 180.16 ÷ 10, accounting for the per-decilitre
versus per-litre difference. For example, a meter reading of 100 mg/dL equals
100 ÷ 18.018 ≈ 5.6 mmol/L.
Worked conversions
| Reading (mg/dL) | Equivalent (mmol/L) | Context |
|---|---|---|
| 54 | 3.0 | Hypoglycaemia (low) |
| 70 | 3.9 | Lower end of normal fasting |
| 100 | 5.6 | Upper end of normal fasting |
| 126 | 7.0 | Fasting diabetes diagnostic threshold |
| 140 | 7.8 | Post-meal pre-diabetes threshold |
| 180 | 10.0 | Common CGM alert level |
| 200 | 11.1 | Random/post-load diabetes threshold |
| 270 | 15.0 | Significantly elevated |
Divide any mg/dL value by 18 (close enough for mental arithmetic) to get a quick mmol/L approximation. For precise clinical documentation, use the full 18.018 factor.
Why two unit systems exist
The United States, Germany, France, and several other countries adopted mg/dL because it expresses glucose as a mass concentration (milligrams of glucose per decilitre of blood), which was the most practical measurement for early clinical chemistry analysers. The UK, Canada, Australia, New Zealand, and most of Europe adopted mmol/L, the SI standard unit for substance concentration.
Both measure the same thing and there is no clinical advantage to either system. The divergence is historical and shows no sign of converging — glucose meters sold in different countries use different units, and guidelines and research literature from different countries cite different numbers for the same clinical thresholds.
This is why international patients, travellers, and clinicians working across borders encounter conversion confusion regularly. A patient’s UK meter reading of 7.0 mmol/L is not 7 in “American units” — it is 126 mg/dL, a value with very different clinical significance.
Reference values in both units
| Category | mg/dL | mmol/L |
|---|---|---|
| Normal fasting | 70–100 | 3.9–5.6 |
| Impaired fasting (pre-diabetes) | 100–125 | 5.6–6.9 |
| Diabetes (fasting, diagnostic) | 126 or above | 7.0 or above |
| Normal 2-hour post-meal | Below 140 | Below 7.8 |
| Pre-diabetes 2-hour post-meal | 140–199 | 7.8–11.0 |
| Diabetes 2-hour post-meal | 200 or above | 11.1 or above |
| Hypoglycaemia | Below 70 | Below 3.9 |
These are widely cited thresholds from diabetes clinical guidelines. Individual laboratory reference ranges and treatment targets vary by patient and clinical context — always interpret results against your own laboratory’s reference range and your clinician’s guidance.
This tool vs HbA1c
This converter handles point-in-time blood glucose readings — the value from a finger-prick meter or a fasting blood draw. It is not for HbA1c (glycated haemoglobin), which is a different test that reflects average glucose over approximately 2–3 months and uses entirely different units (percentage in the US, or mmol/mol in the UK and internationally). HbA1c requires its own conversion table and is not interchangeable with single-point glucose readings.
All calculations run in your browser and the values you enter are never transmitted to any server.