How this calculator works
This calculator converts a blood glucose reading between milligrams per deciliter (mg/dL), the unit used in the United States, and millimoles per liter (mmol/L), the unit used in the UK, Canada, Australia and most of the rest of the world. The conversion is an exact arithmetic factor, so there is no rounding uncertainty in the math itself — only in how precisely you know the original reading.
This tool gives a general reference only. It is not medical advice and cannot diagnose diabetes, prediabetes, or any other condition. The reference values shown below are commonly discussed round numbers, not a substitute for the specific ranges your doctor or lab report uses, which can vary by test type (fasting, post-meal, random) and by individual clinical guideline.
The formula
mmol/L = mg/dL ÷ 18.0182mg/dL = mmol/L × 18.018218.0182 is the standard conversion factor between the two units for glucose, the same constant this site's A1C calculator uses to convert estimated average glucose. The conversion is exact; only the precision of the original reading limits the result.
Worked example: 126 mg/dL
- Start with a reading of 126 mg/dL.
- Divide by 18.0182: 126 ÷ 18.0182 ≈ 6.99 mmol/L.
- Rounded to one decimal place, that is about 7.0 mmol/L.
- Going the other way, 7.0 mmol/L × 18.0182 ≈ 126.1 mg/dL, matching the original reading.
Frequently asked questions
Is 100 mg/dL the same as 5.5 mmol/L?
Very close. 100 ÷ 18.0182 ≈ 5.55 mmol/L, commonly rounded to 5.5 or 5.6 depending on the source. The small difference comes from rounding, not from any ambiguity in the conversion factor itself.
Why do some countries use mg/dL and others mmol/L?
It is a historical difference in laboratory convention. The US, and a handful of other countries, report glucose as a mass concentration (mg/dL); most of the rest of the world reports it as a molar concentration (mmol/L), which is one mole of glucose per liter of blood.
Can this tell me if my blood sugar is normal?
No. This tool only converts units. Reference ranges depend on whether the reading is fasting, post-meal, or random, on the testing method, and on your individual health history — all of which require a doctor's interpretation, not a calculator.
Why does the reference table say 'general reference' instead of giving a clear normal range?
Different clinical guidelines draw the lines in slightly different places, and the right range for one person (for example, someone managing diabetes with medication) can differ from another. The table exists to help you sanity-check a conversion against familiar round numbers, not to diagnose anything.
How is this different from the A1C calculator?
This tool only converts units for a single glucose reading. The A1C calculator estimates average glucose over roughly three months from an A1C blood test percentage, using a separate research-derived formula. Use this converter for a single meter or lab reading, and the A1C tool for a lab A1C result.