Blood Sugar Levels: The Common Units Explained

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When managing blood sugar, you’ll encounter different units depending on where you are in the world. In Sweden and many parts of Europe, we use mmol/L (millimoles per litre), while in the United States, they measure blood sugar using mg/dL (milligrams per decilitre).

Alongside these short-term measurements, there is also a long-term indicator called HbA1C, which provides an overview of your average blood sugar over the past two to three months.

Blood Sugar Measurement Units
Figure 1: Blood Sugar Units - Commonly used blood sugar units in different countries.

Common Units Around the World

Different countries use different units for measuring blood sugar:

  • mmol/L (millimoles per litre): Used in Europe, Canada, Australia, and New Zealand.
  • mg/dL (milligrams per decilitre): Commonly used in the United States and Japan.

Converting Between mmol/L and mg/dL

The conversion is straightforward:

  • To convert from mmol/L to mg/dL: Multiply by 18.
  • To convert from mg/dL to mmol/L: Divide by 18.

For example, if your blood sugar is 5.2 mmol/L, the equivalent in mg/dL would be:

5.2 × 18 = 93.6 mg/dL

Blood Sugar Conversion
Figure 2: Blood Sugar Conversion - Example showing how to convert between mmol/L and mg/dL.

What About Long-Term Blood Sugar? HbA1c (%) and mmol/mol

In addition to daily measurements of blood sugar, there’s also a long-term indicator called HbA1c, which reflects your average blood sugar levels over the past 2-3 months. HbA1c is measured as a percentage (%) in the U.S., but many other countries, including Sweden, the UK, and parts of Europe, measure it in mmol/mol (millimoles per mole).

HbA1c targets can vary depending on your healthcare provider and country. In Sweden and much of Europe, an HbA1c target of around 45 mmol/mol (about 6.3%) is typical for people managing diabetes. In the U.S., the target is often set at 7%, but guidelines may vary depending on the patient’s health status. Always consult with your healthcare provider for a target that suits your specific needs.

The two units are closely related, and you can convert between them using the following formulas:

  • To convert HbA1c % to mmol/mol:
    HbA1c (mmol/mol) = (HbA1c % - 2.15) × 10.929
  • To convert HbA1c mmol/mol to %:
    HbA1c (%) = (HbA1c mmol/mol × 0.09148) + 2.15

For example, an HbA1c of 7% is equivalent to 53 mmol/mol, and an HbA1c of 45 mmol/mol is approximately 6.3%.

HbA1c Measurement
Figure 4: HbA1c (%) and mmol/mol - How to measure long-term blood sugar levels using both % and mmol/mol units.

Warning High School Chem - Incoming Warning

Let’s break down why we multiply or divide by 18 when converting between mmol/L and mg/dL. The difference has to do with the molecular weight of glucose and the way different units measure glucose in the blood.

Molecular weight of glucose: Glucose (C₆H₁₂O₆) has a molecular weight of 180.16 grams per mole. This is important when converting between units.

mmol/L vs. mg/dL: mmol/L measures the concentration of glucose molecules in the blood, while mg/dL measures the weight of glucose in a specific volume of blood.

Here’s the formula to make it easy:

  • 1 millimole of glucose weighs 180.16 mg.
  • 1 litre = 10 decilitres.
  • So, to convert mmol/L to mg/dL, multiply by 18 to account for these factors.

And that’s why we use 18 in the conversion.

Understanding Blood Sugar Units
Figure 4: It's just biochemistry - You don't need the chemistry to do the conversions, they're easy enough to do here.