mg/dL to mmol/L: how to convert a blood sugar reading

A reading of 140 mg/dL and a reading of 7.8 mmol/L describe the same blood sugar level in different units. The United States reports glucose in mg/dL, while the UK, Canada, and Australia use mmol/L, so one short calculation lets you read either format.

Convert your reading with our blood sugar converter and check the math below if you want to do it by hand.

Why glucose has two units

Milligrams per deciliter (mg/dL) reports glucose as a mass in a volume of blood. Millimoles per liter (mmol/L) reports it as an amount of substance in a volume of blood. Both describe the same sample. They differ only in scale, the way inches and centimeters differ.

Laboratories and meters in the United States use mg/dL, which is the unit you will see on the CDC diabetes testing page and the NIDDK blood glucose test page. In the UK, Canada, and Australia, glucose appears in mmol/L, which is the unit used on the Diabetes UK blood sugar levels page. Many meters let you choose either unit in settings, so confirm which unit your device uses before you compare its number with a result from another country or article.

How the conversion works

For glucose, the number 18 links the two units. Use one direction or the other, never both in the same step.

mmol/L = mg/dL ÷ 18

mg/dL = mmol/L × 18

Round mmol/L results to one decimal place and mg/dL results to a whole number. That matches how most meters and lab reports display each unit, and it keeps small rounding differences from looking like real changes.

Worked example: 140 mg/dL and 7.8 mmol/L

Take a meter reading of 140 mg/dL and convert it to mmol/L:

• Start with 140 mg/dL.
• Divide by 18: 140 ÷ 18 = 7.777…
• Round to one decimal place: 7.8 mmol/L.

Now reverse the calculation to check it:

• Start with 7.8 mmol/L.
• Multiply by 18: 7.8 × 18 = 140.4.
• Round to a whole number: 140 mg/dL.

The small gap between 140 and 140.4 comes from rounding 7.777 to 7.8. When you convert with the full decimal, the two directions agree exactly. Round only at the end.

What common readings look like in both units

The table below applies the same divide-by-18 step to readings you may see often. Use it to sense-check a conversion rather than to judge whether a result is good for you.

mg/dL	mmol/L
70	3.9
100	5.6
126	7.0
140	7.8
180	10.0
200	11.1

If your result falls between two rows, divide or multiply the exact number instead of guessing from the nearest row. A meter that reads 155 mg/dL converts to 8.6 mmol/L, which sits between table rows but follows the same rule.

This is not an A1C conversion

A1C is a percentage that reflects average blood sugar over weeks. Its math is separate from the divide-by-18 unit change for a single meter or lab reading.

If you hold a lab slip that says A1C 7 percent, do not divide 7 by 18. Use our A1C calculator instead, and read our A1C to blood glucose conversion guide to see why an estimated average can differ from your daily meter readings.

Mistakes that change the number

Converting in the wrong direction is the usual slip. Multiplying 140 mg/dL by 18 gives 2,520, which no meter would display. If your answer looks wildly high or low, you likely multiplied when you should have divided, or the reverse.

Glucose uses 18. Cholesterol and triglycerides use different factors. Applying a lipid conversion to a glucose reading gives a wrong answer, so keep each test with its own factor.

Mixing units inside one comparison also misleads. A fasting result of 5.6 mmol/L and a post-meal result of 140 mg/dL look far apart until you convert: 5.6 times 18 is about 101 mg/dL. Convert both readings to one unit first, then compare.

Check the meter setting itself. A device set to mmol/L that shows 7.8 is normal display behavior, not a dangerously low 7.8 mg/dL. The unit printed beside the number is part of the result.

Limitations of a converted reading

Conversion changes the unit, not the quality of the measurement. Home meters have allowed error bands, test strips age, and a reading taken after food differs from one taken after an overnight fast. Dividing by 18 cannot correct any of that. It restates the same result with the same limits.

One converted reading also cannot diagnose diabetes or set a treatment target on its own. The CDC and NIDDK testing pages describe blood glucose tests as part of a clinical picture that includes repeat tests, A1C, symptoms, and history. Diabetes UK presents mmol/L ranges with that same testing context. If a converted number surprises you, repeat the test under the conditions your care team advised and bring the full pattern, with units labeled, to your visit.

For the arithmetic itself, trust the converter: enter the value, confirm the unit, and read the result in our blood sugar converter.