Blood glucose converter — mg/dL to mmol/L and back

How to use the blood glucose converter

1. Type your reading in Value.
2. In From, choose the unit your meter, lab report or app uses: mg/dL or mmol/L.
3. In To, choose the other unit. The converted value appears at once.
4. Use the swap button to turn the direction round, and read the Reference conversions table for 12 common values from 54 to 300 mg/dL.

What it does and when to use it

Glucose is measured in two units around the world. A reading of 5.5 on a UK meter and 99 on a US meter describe the same blood sugar. You need to convert when you read a guide, study or forum post written for the other system, travel with a meter bought abroad, or share logs with a clinic that uses the other unit.

This page does a unit change and nothing else. It does not judge whether a number is high or low. For other health figures, the BMI calculator and the blood pressure calculator work the same way: a number in, a plain answer out.

How it works

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

The factor comes from the molar mass of glucose, C6H12O6. One mmol/L means 1 millimole per litre. Multiply by the molar mass in g/mol to get mg per litre, then divide by 10 to get mg per decilitre. With 180.182 g/mol that gives 18.0182.

18.0182 is a long-standing convention in medical conversion tables. The NIST Chemistry WebBook gives glucose a molecular weight of 180.1559, which would give 18.0156. The two differ by about 0.014%, far less than the accuracy of any home meter, so either answer is fine in practice. The tool uses 18.0182 throughout, including in the reference table, which rounds mmol/L to one decimal place.

Worked examples

A US-style reading. 100 mg/dL = 5.54994394557 mmol/L. A meter would show 5.5.

A UK-style reading. 7.8 mmol/L = 140.54196 mg/dL, shown on a US meter as 141 (or 140 in many tables).

Round trip. 5.5 mmol/L = 99.1001 mg/dL. Going back from 99 mg/dL gives 5.49 mmol/L, so small differences after rounding are normal and do not mean the meter is wrong.

Limits and tips

• Round like your meter does. Meters show mg/dL as whole numbers and mmol/L to one decimal. A 12-digit result does not make a reading more accurate.
• Lab values are sometimes plasma and sometimes whole blood. That difference is not a unit issue and this tool does not adjust for it.
• To change other units, try the weight converter for grams and ounces or the volume converter for decilitres and litres.