Blood Sugar Converter (mg/dL ⇄ mmol/L) & Level Chart

Two independent things happen when you enter a reading: a unit conversion and a diagnostic classification. Both are exact lookups — there are no assumptions or user-supplied rates.

Unit conversion. Blood glucose in mmol/L is a molar concentration; in mg/dL it is a mass concentration. Glucose (C₆H₁₂O₆) has a molar mass of 180.156 g/mol, so a 1 mmol/L solution holds 180.156 mg of glucose per litre, i.e. 18.0156 mg per decilitre. Clinical tables conventionally round this to 18.0182 mg/dL per mmol/L, which this tool adopts so its numbers match printed charts:

• mmol/L = mg/dL ÷ 18.0182
• mg/dL = mmol/L × 18.0182

The two factors (18.0182 tabulated vs 18.0156 from molar mass) differ by less than 0.15%, so any reading converts the same to one decimal place. The internal value is kept unrounded; only the display is rounded — mg/dL to a whole number, mmol/L to one decimal.

Classification.The reading is normalised to mg/dL and compared against the published thresholds for the test you pick. The American Diabetes Association Standards of Care define fasting plasma glucose as normal below 100 mg/dL, prediabetes (Impaired Fasting Glucose) at 100–125 mg/dL, and diabetes at 126 mg/dL and above. For the 2-hour value in a 75 g oral glucose tolerance test, normal is below 140 mg/dL, prediabetes (Impaired Glucose Tolerance) is 140–199 mg/dL, and diabetes is 200 mg/dL and above. A random reading has no formal “normal” band; 200 mg/dL or more with classic symptoms is a diabetes-range flag, and 140–199 is shown as borderline with a prompt to confirm using a fasting test or OGTT.

Where the WHO differs — it starts the fasting prediabetes band at 110 mg/dL (6.1 mmol/L) rather than 100 — the tool adds a note so you see both interpretations. The diabetes cutoffs (126 and 200 mg/dL) are shared by both bodies. HbA1c bands appear in the chart for reference only; average-glucose conversion is handled by the separate A1C calculator, which this page links to rather than duplicate.

• American Diabetes Association — Standards of Care in Diabetes (2025), Section 2: Diagnosis and Classification
• WHO — Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia (2006)
• WHO — Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus (2011)

The conversion factor and diagnostic ranges on this page were last cross-checked against the ADA and WHO documents on 2026-07-11. They are reviewed whenever the ADA publishes a new Standards of Care edition (annually) or WHO revises its criteria.