Blood Sugar Units: Converting mmol/L to mg/dL
Blood glucose is measured in millimoles per litre (mmol/L) in most countries including the UK, Australia, and Canada, and in milligrams per decilitre (mg/dL) in the United States, Germany, and several other countries. The two units measure the same thing — just on different scales.
Conversion Formula
mg/dL to mmol/L: value ÷ 18.0182
mmol/L to mg/dL: value × 18.0182Quick Reference Table
- 3.9 mmol/L = 70 mg/dL (low normal / hypoglycaemia threshold)
- 5.0 mmol/L = 90 mg/dL (fasting normal)
- 5.6 mmol/L = 100 mg/dL (upper fasting normal / pre-diabetes threshold in US)
- 7.0 mmol/L = 126 mg/dL (fasting diabetes threshold)
- 7.8 mmol/L = 140 mg/dL (2-hr post-meal normal upper limit)
- 11.1 mmol/L = 200 mg/dL (2-hr post-meal diabetes threshold)
HbA1c: The 3-Month Average
HbA1c reflects average blood glucose over 3 months. Targets:
- Normal: <5.7% (US) / <39 mmol/mol (UK)
- Pre-diabetes: 5.7–6.4% / 39–47 mmol/mol
- Diabetes: ≥6.5% / ≥48 mmol/mol
Convert blood glucose values instantly: Free Blood Sugar Converter
The Conversion Factor: mmol/L and mg/dL
To convert mmol/L to mg/dL, multiply by 18.0182. To convert mg/dL to mmol/L, divide by 18.0182 (or multiply by 0.0555). This factor comes from the molecular weight of glucose (180.182 g/mol). Examples: 5.0 mmol/L = 90 mg/dL; 7.0 mmol/L = 126 mg/dL; 10.0 mmol/L = 180 mg/dL. Most clinical literature and glucometers sold in the UK, Australia, and Canada use mmol/L; US devices use mg/dL.
Clinical Reference Ranges
- Fasting normal: 3.9–5.5 mmol/L (70–99 mg/dL)
- Prediabetes (fasting): 5.6–6.9 mmol/L (100–125 mg/dL)
- Diabetes diagnosis (fasting): ≥7.0 mmol/L (≥126 mg/dL) on two separate tests
- 2-hour post-meal normal: <7.8 mmol/L (<140 mg/dL)
- Hypoglycaemia (low): <3.9 mmol/L (<70 mg/dL)
- Severe hypoglycaemia: <2.8 mmol/L (<50 mg/dL)
Frequently Asked Questions
Why do different countries use different units?
The United States adopted mg/dL from older laboratory conventions. Most other countries adopted the SI unit (mmol/L) during metrication in the 1970s–80s. Both are correct measures of the same thing — the mass of glucose per unit volume of blood. Medical devices are calibrated to the local standard, so a US glucometer reads in mg/dL while a UK device reads in mmol/L.
What blood sugar level requires immediate medical attention?
Severe hypoglycaemia (below 2.8 mmol/L / 50 mg/dL) or hyperglycaemia above 27.8 mmol/L (500 mg/dL) are medical emergencies requiring immediate treatment. Anyone with symptoms of confusion, loss of consciousness, or extreme thirst with high readings should seek emergency care regardless of the specific number.
Is HbA1c the same as blood glucose?
No. HbA1c (glycated haemoglobin) reflects average blood glucose over the preceding 2–3 months. It is expressed as a percentage (e.g., 7%) or in mmol/mol (e.g., 53 mmol/mol) and is not directly converted to mg/dL or mmol/L. Separate conversion charts exist for HbA1c.