Blood Sugar Converter

This is the quick one. No Calculate button, no direction to pick first, nothing to set up. If you have a column of readings from a foreign lab to get through, or a meter stuck on the wrong unit, that saves more clicks than it sounds like it would.

Blood glucose is measured in two different units depending on the country.

mg/dL (milligrams per deciliter) is used in the United States, Japan, France, Egypt, and Colombia. mmol/L (millimoles per liter) is used in the UK, Canada, Australia, China, and most of Europe.

Conversion formula:

• mmol/L = mg/dL ÷ 18.0156
• mg/dL = mmol/L × 18.0156

The factor 18.0156 comes from the molar mass of glucose (180.156 g/mol) divided by 10, since mg/dL is per decilitre and mmol/L per litre.

Plenty of references print 18.0182 instead. It does not come out of the molar mass, and the difference is 0.014%, which at the 126 mg/dL diabetes threshold is roughly a thousandth of a mmol/L. Every glucose page on this site uses 18.0156, so their answers line up. None of this is visible on a meter anyway: ISO 15197 allows home meters a 15% margin, which is a thousand times larger than the argument.

The other two glucose pages, and which one you actually want. This page converts and gets out of the way. The blood glucose unit converter is the long read: why two units exist at all, what pushes glucose up and down, how continuous monitors lag behind blood, where HbA1c stops being reliable. And normal blood sugar levels by time of test does the thing no plain converter can, which is ask when the sample was taken before telling you whether the number is fine, because 145 fasting and 145 after lunch are not the same news.

Common reference ranges (fasting):

The two units exist because they measure glucose differently. mg/dL counts the mass of glucose in a volume of blood, while mmol/L counts the number of glucose molecules. Both are valid, they just answer slightly different questions, which is why the conversion runs through glucose’s molecular weight.

In practice the gap matters most when you’re reading advice or a meter set to the other country’s unit. A fasting reading of 90 mg/dL is 5.0 mmol/L, and the diabetes threshold of 126 mg/dL is 7.0 mmol/L. The numbers look wildly different, so it’s easy to misread a perfectly normal value as alarming, or the reverse. This is general information for converting between units, not medical advice; for anything about your own health, talk to a doctor.