mmol/L vs mg/dL: Blood Glucose Units Explained
Blood glucose is measured in mmol/L (most of the world) or mg/dL (mainly the United States). To convert, multiply mmol/L by 18 to get mg/dL, or divide mg/dL by 18 to get mmol/L. Keep your target, your readings, and your correction factor all in the same unit so the math stays correct.
Two units, the same measurement
mmol/L (millimoles per litre) and mg/dL (milligrams per decilitre) are two ways of writing the same thing: the concentration of glucose in your blood. Canada, the UK, Australia, and most of the world use mmol/L, while the United States and a few other countries use mg/dL.
Neither unit is more accurate — they are just different scales, the way kilometres and miles both measure distance. A reading of 6 mmol/L and a reading of 108 mg/dL describe the same blood glucose level.
How to convert between them
The conversion factor is 18. To go from mmol/L to mg/dL, multiply by 18: 6 mmol/L × 18 ≈ 108 mg/dL. To go from mg/dL to mmol/L, divide by 18: 180 mg/dL ÷ 18 = 10 mmol/L.
Results are usually rounded — mmol/L to one decimal place and mg/dL to a whole number — so a converted value may differ slightly from what a meter set to that unit would display, but it is close enough for everyday understanding.
Why consistency matters for dosing
A correction dose is calculated as (current glucose − target) ÷ correction factor. If your reading is in mg/dL but your target or correction factor is in mmol/L, the result is meaningless and can be dangerously wrong. Always keep your reading, target, and correction factor in the same unit.
If you switch meters, apps, or move between countries, double-check which unit each tool is using before you rely on any calculation.
How CarbTrack handles units
CarbTrack lets you choose your preferred unit and keeps your glucose readings, targets, and correction factor consistent within it, so corrections are calculated on a single scale. It is a calculator that works in the unit you set — it does not measure glucose or convert your care plan for you. Confirm your settings match the unit your provider uses.
Step by step
- Identify your current unit Check whether your reading is in mmol/L or mg/dL — your meter, app, or care plan will tell you.
- Apply ×18 or ÷18 Multiply mmol/L by 18 to get mg/dL, or divide mg/dL by 18 to get mmol/L.
- Use the same unit everywhere Make sure your reading, target, and correction factor are all in the same unit before doing any dose math.
Frequently asked questions
How do I convert mmol/L to mg/dL?
Multiply the mmol/L value by 18. For example, 6 mmol/L × 18 ≈ 108 mg/dL. To go the other way, divide mg/dL by 18.
Why are there two different units for blood sugar?
They are different measurement scales for the same thing. Most of the world reports glucose in mmol/L, while the United States uses mg/dL — like kilometres versus miles.
Does it matter which unit I use in a calculator?
It matters that everything is in the same unit. Mixing mmol/L and mg/dL in a correction calculation gives a wrong result, so keep your reading, target, and correction factor consistent.
Sources
CarbTrack does this math for you — instantly, from a photo or a food search.
Download CarbTrackCarbTrack is a calculator tool only. Not a medical device. Not medical advice. Insulin dose calculations are based solely on the carb ratio you provide. Always consult your healthcare provider before making changes to your insulin regimen or diabetes management plan.