Glucose Unit Converter
Glucose Unit Converter
Convert blood glucose between mg/dL, mmol/L and g/L, with the diagnostic thresholds in both units and the two pre-analytical traps that move the number.
Glucose converter
mg/dL ⇄ mmol/LBlood glucose 126 mg/dL, fasting
Formula and conversion factor
mg/dL = mmol/L × 18.02
g/L = mg/dL × 0.01
- 0.0555
- one decilitre of plasma holds 0.01 g per mg/dL, and glucose has a molecular mass of 180.16, so 0.01 ÷ 180.16 = 55.5 µmol/L per mg/dL
- 18.02
- the reciprocal; the familiar shortcut of dividing mg/dL by 18 is accurate to about one part in 900
- g/L
- used in parts of continental Europe; 1 g/L is 100 mg/dL, so a fasting threshold of 126 mg/dL is 1.26 g/L
- plasma vs whole blood
- plasma glucose reads about 11% higher than whole blood at a normal haematocrit; all diagnostic thresholds are plasma values
Worked example
Blood glucose 126 mg/dL, fasting
126 × 0.0555074 = 6.99 mmol/L
126 × 0.01 = 1.260 g/L
The exact conversion gives 6.99, not 7.00 — the paired thresholds of 126 mg/dL and 7.0 mmol/L are each rounded conventions, since 7.0 mmol/L is 126.1 mg/dL
At the fasting diagnostic threshold, and above the fasting reference interval of 70–99 mg/dL
Diagnostic thresholds in both units
| mg/dL | mmol/L | |
|---|---|---|
| Fasting, normal | 70 – 99 | 3.9 – 5.5 |
| Impaired fasting glucose | 100 – 125 | 5.6 – 6.9 |
| Diabetes, fasting | ≥ 126 | ≥ 7.0 |
| Impaired glucose tolerance, two-hour | 140 – 199 | 7.8 – 11.0 |
| Diabetes, two-hour or random with symptoms | ≥ 200 | ≥ 11.1 |
| Hypoglycaemia, conventional cut-off | < 70 | < 3.9 |
What moves the number before it reaches the analyser
| Effect | Direction | Size |
|---|---|---|
| Plasma rather than whole blood | Plasma higher | About 11% at a normal haematocrit |
| Delay before separation, plain or EDTA tube | Falls | Roughly 5 – 7% per hour at room temperature |
| Fluoride-oxalate tube | Stabilises, but slowly | Glycolysis continues for up to an hour before fluoride takes full effect |
| Capillary sample after a meal | Higher than venous | Up to 20 – 25 mg/dL in the post-prandial period |
Why the same patient gives different glucose numbers
Blood glucose is reported in mg/dL in the United States and much of Asia, in mmol/L across the United Kingdom, Europe and Australasia, and occasionally in g/L in parts of continental Europe. The factor of 0.0555 between mg/dL and mmol/L comes straight from the molecular mass of glucose, 180.16: a milligram per decilitre is 0.01 g/L, and dividing that by 180.16 gives 55.5 µmol/L. Dividing mg/dL by 18 is the bedside shortcut and is accurate to about one part in 900.
The thresholds are worth holding in both conventions, because they are the numbers that define the diagnosis. Fasting plasma glucose of 126 mg/dL, or 7.0 mmol/L, is the diabetic threshold; 200 mg/dL, or 11.1 mmol/L, is the threshold for a random or two-hour value. Between 100 and 125 mg/dL, or 5.6 to 6.9 mmol/L, is impaired fasting glucose. These are venous plasma figures, and outside unequivocal hyperglycaemic symptoms a diagnosis requires a confirmed result rather than a single reading.
Two pre-analytical effects explain most of the disagreements clinicians see. The first is the sample matrix: plasma glucose runs about 11% higher than whole blood at a normal haematocrit, because red cells contain less water than plasma and glucose distributes in water. Modern meters report plasma-equivalent values to hide this, but the correction is applied to a whole-blood measurement, so a meter and a laboratory can differ while both are right.
The second is glycolysis in the tube. Red cells and leucocytes keep consuming glucose after venepuncture, and in an untreated sample the concentration falls by roughly 5 to 7% per hour at room temperature. A specimen that sat overnight reads low enough to reclassify a patient from diabetes to impaired fasting glucose. Fluoride-oxalate tubes limit this but do not stop it immediately, since fluoride acts late in the glycolytic pathway; prompt separation, or a citrate-fluoride tube, is more reliable.
Frequently asked questions
How do I convert glucose from mg/dL to mmol/L?
Multiply by 0.0555, or divide by 18 for a close approximation. A glucose of 126 mg/dL is 6.99 mmol/L. The paired diagnostic thresholds of 126 mg/dL and 7.0 mmol/L are each rounded, since 7.0 mmol/L is strictly 126.1 mg/dL.
What are the diagnostic thresholds for diabetes?
A fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or above, or a two-hour or random value of 200 mg/dL (11.1 mmol/L) or above. Fasting values of 100 to 125 mg/dL (5.6 to 6.9 mmol/L) indicate impaired fasting glucose. Confirmation on a second sample is needed unless hyperglycaemic symptoms are unequivocal.
Why does my meter disagree with the laboratory?
Meters measure whole blood and report a plasma-equivalent value, and plasma glucose is about 11% higher than whole blood at a normal haematocrit. Capillary samples also run higher than venous ones after a meal. Both results can be correct at the same time.
Does a delayed sample change the glucose result?
Yes, and substantially. Cells in the tube continue to metabolise glucose, lowering the concentration by roughly 5 to 7% per hour at room temperature in an untreated sample. Fluoride-oxalate slows this, but it acts late in the glycolytic pathway, so prompt separation still matters.
What is glucose in g/L?
One gram per litre is 100 mg/dL, so the fasting diagnostic threshold of 126 mg/dL is 1.26 g/L and 200 mg/dL is 2.00 g/L. The unit appears mainly on reports from parts of continental Europe.
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References
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S20–S42.
- Sacks DB, Arnold M, Bakris GL, et al. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem. 2011;57(6):e1–e47.
- World Health Organization. Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia. WHO; 2006.