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Free health tool

Blood glucose unit converter

Convert a blood glucose reading between mmol/L and mg/dL in seconds, without adding targets, labels or diagnosis.

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  • Instant result
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Calculate your result

Enter the number exactly as it appears on the source report, meter or app.

Accepted range: 0 to 100 mmol/L

Your result will appear here

Nothing is saved or added to the URL.

What this result means

Choose the unit shown on your glucose result, enter the value, and the converter will express the same concentration in the other unit. It uses the NIST glucose molecular mass for the calculation; the familiar multiply-or-divide-by-18 rule is a rounded shortcut. [1]

What mmol/L and mg/dL mean

Both units describe glucose concentration. mmol/L expresses the amount of glucose substance in a litre; mg/dL expresses glucose mass in a decilitre. A conversion changes the unit, not the underlying concentration. [1][3]

Why the conversion factor is about 18

NIST reports a glucose molecular mass of 180.156 g/mol. After matching millimoles with milligrams and converting one litre to ten decilitres, the factor is 18.0156. Public health tables often round this to 18 or use the reciprocal 0.0555 for quick conversion. [1][2][3]

What the conversion cannot tell you

The result carries forward the source reading. It does not know when or how the glucose was measured, whether the source was a laboratory, meter or sensor, or what range is appropriate for an individual.

This converter accepts a glucose concentration only. It cannot accept an HbA1c percentage, HbA1c mmol/mol, estimated average glucose or glucose management indicator value.

Safe next steps

Keep the original reading and unit beside the converted number. If the value will affect treatment, insulin, medication or an urgent decision, use the original device or laboratory result and follow the plan from the treating health professional rather than relying on a web conversion alone.

Formula and assumptions

Formula
mg/dL = mmol/L × 18.0156. mmol/L = mg/dL ÷ 18.0156. The factor is the NIST glucose molecular mass, 180.156 g/mol, divided by 10 to change litres to decilitres. [1]
Version
NIST glucose mass-to-amount unit conversion, nist-sp-260-253-glucose-v1
Rounding
Calculate with the full stored factor, then round once for display: one decimal place for mg/dL and two decimal places for mmol/L. The unrounded source value is not changed.
Worked example
For 5.5 mmol/L: 5.5 × 18.0156 = 99.0858 mg/dL, displayed as 99.1 mg/dL. Converting 99.1 mg/dL back gives 5.50 mmol/L after display rounding. [1]

Who this is for — and when not to use it

Intended use

Neutral, reversible unit conversion for a person who already has a blood glucose concentration in mmol/L or mg/dL and needs the equivalent display unit.

Not intended for

This tool does not interpret glucose, diagnose diabetes, set a target, convert HbA1c or estimated average glucose, or guide medication, insulin, food, exercise or emergency decisions.

Exclusions

  • Diagnosis or classification of a glucose result
  • Medication or insulin decisions
  • Emergency decisions
  • HbA1c, eAG, GMI or another analyte
  • Changing or correcting the original measurement

Evidence sources

  1. 1. Certification of Standard Reference Material 965c: Glucose in Frozen Human Serum — National Institute of Standards and Technology. Accessed Aug 8, 2026.
  2. 2. Diabetes in America, 3rd Edition — Appendix 1: Conversions — National Institute of Diabetes and Digestive and Kidney Diseases. Accessed Aug 8, 2026.
  3. 3. Diabetes-related common terms — American Diabetes Association. Accessed Aug 8, 2026.