Blood Sugar Converter (mg/dL ⇄ mmol/L)

Understanding the blood sugar converter — concept and principle

Blood glucose is reported in two units around the world. The United States, Korea, Japan and several other countries mostly use milligrams per decilitre (mg/dL); the UK, Canada, Australia and much of Europe use millimoles per litre (mmol/L). Glucose meters, lab reports, guidelines and research papers can use either, so a quick, exact conversion helps when you read foreign guidance, travel with a meter or compare results from different labs.

How it is calculated

• mmol/L = mg/dL ÷ 18.016
• mg/dL = mmol/L × 18.016

The calculator shows mmol/L to two decimals and mg/dL to one decimal. Many references round the factor to 18, which changes results by less than 0.1%.

The principle

mg/dL measures mass: how many milligrams of glucose are in a tenth of a litre of blood plasma. mmol/L counts molecules: how many millimoles are in a litre. To go from one to the other you need the mass of one mole of glucose (C₆H₁₂O₆), about 180.16 g/mol. One mmol of glucose is therefore 180.16 mg. Per litre that is 180.16 mg/L, and since one decilitre is a tenth of a litre, it equals 18.016 mg/dL. The factor applies only to glucose; cholesterol, triglycerides and other substances have different molar masses and different factors.

Worked example

Default input: 100 mg/dL to mmol/L.

1. Divide by the glucose factor: 100 ÷ 18.016 = 5.5506.
2. Round to two decimals: 5.55 mmol/L.
3. Check in reverse: 5.55 × 18.016 ≈ 99.99 mg/dL, i.e. 100 mg/dL.

How to read the result

Commonly cited diagnostic cut-offs for fasting plasma glucose from the American Diabetes Association are: below 100 mg/dL (5.6 mmol/L) normal, 100–125 mg/dL (5.6–6.9 mmol/L) impaired fasting glucose, and 126 mg/dL (7.0 mmol/L) or higher consistent with diabetes when confirmed. A level below 70 mg/dL (3.9 mmol/L) is generally treated as low blood sugar. These thresholds apply to specific tests in specific conditions; a single reading after a meal is interpreted differently.

Common mistakes

• Typing a mmol/L value into the mg/dL direction; a "5.5" read as mg/dL would be dangerously low.
• Using 18 for one value and 18.016 for another and worrying about the tiny difference.
• Trying to convert HbA1c (%) with this factor; HbA1c uses a different scale and formula.
• Comparing a capillary meter reading directly with a laboratory plasma value; small differences are normal.

Frequently asked questions

What is 100 mg/dL in mmol/L?

About 5.55 mmol/L (often rounded to 5.6).

What is 7 mmol/L in mg/dL?

About 126.1 mg/dL.

Why is the factor 18?

Because glucose has a molar mass of about 180 g/mol, and converting litres to decilitres divides by 10.

Which unit does my meter use?

It is shown on the display and in the manual. Many meters are fixed to the unit of the country where they are sold.

Sources: IUPAC, Standard atomic weights (glucose molar mass ≈ 180.16 g/mol) · American Diabetes Association, Standards of Care in Diabetes — Classification and Diagnosis of Diabetes