Blood Sugar mg/dL to mmol/L — Convert and Read It

US meters and labs report glucose in mg/dL. Meters bought abroad, research papers and most other countries use mmol/L. Divide by 18 to go one way, multiply by 18 to come back — so 90 mg/dL is 5.0 mmol/L, and 7.0 mmol/L is 126 mg/dL.

The chart, with the US thresholds in both units

mg/dL	mmol/L	What it lines up with (fasting)
54 mg/dL	3.0 mmol/L	Clinically significant low glucose
70 mg/dL	3.9 mmol/L	Bottom of the usual normal range
99 mg/dL	5.5 mmol/L	Top of the usual normal range
100 mg/dL	5.6 mmol/L	Prediabetes begins
125 mg/dL	6.9 mmol/L	Top of the prediabetes band
126 mg/dL	7.0 mmol/L	Diabetes threshold
180 mg/dL	10.0 mmol/L	Common post-meal target ceiling
200 mg/dL	11.1 mmol/L	Random-glucose diagnostic level

Notice how clean the mmol/L column is at the important lines: 3.9, 5.6, 7.0, 11.1. That is not a coincidence of the conversion. Several of these cutoffs were set in mmol/L and then converted into the mg/dL numbers Americans memorise — 7.0 became 126, and 11.1 became 200.

Two decimal places you can throw away

A glucose meter is allowed meaningful error. Under ISO 15197, the accuracy standard home meters are validated against, a device passes if 95 percent of its readings at or above 100 mg/dL land within 15 percent of a laboratory value — about 15 mg/dL, or 0.8 mmol/L, at a reading of 100 — and within 15 mg/dL below that.

So a converted figure of “5.56 mmol/L” is precision theatre. One decimal place in mmol/L, or whole numbers in mg/dL, is already finer than the reading it came from. The practical consequence: do not read anything into a 2 mg/dL move between two fingersticks, in either unit.

The two conversions people confuse

Diabetes care produces three numbers that all describe glucose and convert three different ways.

• Glucose concentration, the one on this page: divide mg/dL by 18.
• Hemoglobin A1c, a percentage of glycated hemoglobin, which converts to the international mmol/mol unit through its own formula and is not a concentration at all.
• Estimated average glucose, which is A1c translated into an average glucose by regression, not by unit conversion. It is a different quantity that happens to be printed in the same units as a fingerstick.

Applying the factor 18 to an A1c of 7 gives 126, which looks like a familiar number and is meaningless. The look-alike is the whole trap.

When a foreign meter is the reason you are here

If you bought a meter overseas or are using one someone brought back, check the display unit before you act on a reading — most devices let you switch, and some do not. A meter set to mmol/L showing 5.0 next to a US target of 100 is not a low reading; it is the same reading.

Where readings feel inconsistent, remember that fingerstick glucose and lab plasma glucose are not interchangeable to the last digit either, and that diagnosis in the US rests on lab testing rather than on a home meter.

The other unit on a routine blood panel that Americans convert is cholesterol, and it uses a completely different factor — see cholesterol mg/dL to mmol/L. For the weight that most medication doses are calculated from, pounds to kg.

This content is informational, converts units only, and does not replace medical interpretation of a glucose result.