Blood Sugar Converter

How it is calculated

Glucose is reported either in mg/dL or in mmol/L, and the tool converts with the factor 18.018: mmol/L = mg/dL ÷ 18.018 and mg/dL = mmol/L × 18.018. The direction setting says which unit you typed; the mg/dL result is shown to one decimal and the mmol/L result to two. For the range label the value is first expressed in mg/dL, then compared with fixed fasting limits: below 100 is the normal range, 100 up to but not including 126 is the prediabetes range, and 126 or more is the diabetes range. The label assumes a fasting sample; after a meal the same number means something different. Readings that are physically implausible, below 10 mg/dL or above 2000 mg/dL once expressed in mg/dL, show no result at all, and so does zero or a negative number. It does not diagnose anything.

Common mistakes

• Leaving the direction on mg/dL when the number is in mmol/L: 6.1 read as mg/dL is below 10 and now gives no result, while the same 6.1 with the direction set to mmol/L gives 109.9 mg/dL.
• Applying the fasting range label to a reading taken after eating, when higher numbers are expected; the label is only meant for a fasting sample.
• Rounding the factor to 18 for exact work: 18 versus 18.018 shifts a value near a limit, for example 5.6 mmol/L, across the 100 mg/dL line.
• Entering a mmol/L figure with the direction on mmol/L but typing the mg/dL value, for example 112: that is read as 2018 mg/dL, above 2000, and gives no result.
• Treating the label as a diagnosis: values from 10 mg/dL upward that are under 100 are all labelled normal, so a low reading needs separate judgement.