mg/dL and mmol/L: Choosing Your Blood Sugar Units

Two Units for the Same Thing

Blood glucose can be expressed in two units, and they measure the same thing in different ways. mg/dL (milligrams per decilitre) states a mass of glucose in a volume of blood. mmol/L (millimoles per litre) states the number of glucose molecules in a volume of blood. Neither is more correct than the other — they are simply two conventions, and which one you see depends mostly on where you live.

This can be confusing when you come across a number without its unit. A fasting reading of "95" is an ordinary mg/dL value, but "95" in mmol/L would be impossible — typical mmol/L readings sit in the single digits or low teens (a fasting value around 5.3 mmol/L equals about 95 mg/dL). Knowing which unit you are working in keeps you from misreading a number by a factor of eighteen, which is exactly why GlucoLog asks you to choose.

Which Country Uses Which Unit

As a rough guide, the split looks like this:

• mg/dL is standard in the United States, and also common in much of continental Europe, the Middle East, Japan, and many other countries — for example France, Germany, Spain, Italy and much of Latin America and Asia.
• mmol/L is standard across the United Kingdom, Ireland, Canada, Australia, New Zealand, and much of northern and eastern Europe, among others.

These are general patterns rather than strict rules, and some places use both in different settings. What matters in practice is simple: match your app to your meter and your doctor. If your glucose meter shows mmol/L and your clinic talks in mmol/L, set GlucoLog to mmol/L so everything lines up and you never have to convert in your head. If you move between countries or devices that use different units, the conversion below keeps you oriented.

The ×18 Conversion

Converting between the two units is refreshingly simple, because the factor is very close to 18 (more precisely 18.016, but 18 is accurate enough for everyday use):

• mmol/L to mg/dL: multiply by 18. So 5.5 mmol/L × 18 ≈ 99 mg/dL.
• mg/dL to mmol/L: divide by 18. So 180 mg/dL ÷ 18 = 10 mmol/L.

A few familiar landmarks make the scale intuitive: 70 mg/dL ≈ 3.9 mmol/L, 100 mg/dL ≈ 5.6 mmol/L, 140 mg/dL ≈ 7.8 mmol/L, and 180 mg/dL = 10 mmol/L. You rarely need to do this by hand, though — in GlucoLog you simply choose your preferred unit, and every reading, chart and report is shown that way. If you ever switch units, your existing readings are displayed consistently in the unit you have selected, so your history stays easy to read.

This guide is for general information only and is not medical advice — use the unit your doctor and meter use, and talk to your care team about interpreting your numbers.