Blood glucose is reported in two different units depending on where you are: mg/dL in the United States, and mmol/L almost everywhere else. This calculator converts between them precisely and shows how a given reading compares to the standard ADA reference ranges — both as a fasting value and as a post-meal value.
Why two units exist
The United States reports blood glucose in milligrams per deciliter (mg/dL) — a mass-per-volume unit. Most of the rest of the world uses millimoles per liter (mmol/L), the SI unit that describes the actual molar concentration of glucose in the blood. Neither unit is more 'correct' than the other; they're just different conventions that became standard in different health systems, and travelers, researchers, and anyone reading international literature regularly need to convert between them.
How the conversion works
This calculator uses a conversion factor of 18.0182 — divide an mg/dL value by 18.0182 to get mmol/L, or multiply an mmol/L value by 18.0182 to get mg/dL. You'll sometimes see quick mental-math shortcuts (like '÷18' or the commonly quoted '100 mg/dL = 5.6 mmol/L') that use a slightly coarser rounding; this tool always applies the more precise 18.0182 factor, so a careful reader may see the last displayed digit differ by a tenth from a rounded-up textbook value.
Why fasting vs. post-meal context matters
The American Diabetes Association sets different reference bands depending on when a glucose reading was taken. The same raw number — say, 150 mg/dL — sits in the diabetes-range fasting band but only the prediabetes post-meal band. Comparing a reading to the wrong context can lead to the wrong conclusion, which is why the Fasting vs Post-Meal tab classifies the same entered value under both sets of ADA thresholds side by side.