A glucose reading of 100 mg/dL is about 5.6 mmol/L. That one fact explains a lot of confusion: a chart from another country, a meter set to a different unit, a friend abroad quoting numbers that look nothing like yours. Here is where each unit is used, how to convert between them, and a table of common values. This is general information from the sources listed at the end, not advice for your situation.
Why there are two units
In the United States, blood glucose results are reported in mg/dL (milligrams per deciliter), while some other countries use mmol/L (millimoles per liter) [1]. In Canada, for example, blood sugar targets are published in mmol/L [2]. Think of kilometers and miles: the same distance, written two ways.
The conversion: one number, 18
One factor does it all: 18. To convert from mmol/L to mg/dL, multiply by 18; to convert from mg/dL to mmol/L, divide by 18 [1]. For example, 10 mmol/L × 18 = 180 mg/dL, and 180 mg/dL ÷ 18 = 10 mmol/L.
That is why the commonly cited time-in-range band appears in both forms: 70 to 180 mg/dL is 3.9 to 10.0 mmol/L [3]. (See the time in range post.)
Common values side by side
| mg/dL | mmol/L |
|---|---|
| 54 | 3.0 |
| 70 | 3.9 |
| 80 | 4.4 |
| 100 | 5.6 |
| 126 | 7.0 |
| 130 | 7.2 |
| 140 | 7.8 |
| 180 | 10.0 |
| 200 | 11.1 |
| 250 | 13.9 |
The values in the table are not arbitrary. 70 and 180 mg/dL bound the standard time-in-range band, and the consensus paper also sets separate thresholds below 54 mg/dL and above 250 mg/dL [5]. 80 and 130 mg/dL are the before-meal range in US guidance [4]. 100 mg/dL is the lower edge of the fasting prediabetes range, and 126 mg/dL (fasting) and 200 mg/dL are lab thresholds for the diabetes range; 140 mg/dL is the lower edge of the 2-hour glucose tolerance test prediabetes range [6]. It is also the upper edge of the pregnancy time-in-range band [5].
Reading a chart from another country
Each chart states its targets in its own unit, so it takes a conversion to compare them. For most nonpregnant adults, a US chart lists 80 to 130 mg/dL before a meal [4]. A Canadian one lists 4.0 to 7.0 mmol/L for fasting and before meals [2], which converts to roughly 72 to 126 mg/dL. They are close without being identical.
Both also say that targets are individualized. The Canadian chart says blood sugar targets are different for each person and that yours may not match the examples in its chart [2]; the US guidance says targets are individualized based on factors such as how long someone has had diabetes and their age [4]. The numbers to use are the ones your care team gives you.
Same number, different unit
Because the two scales differ by a factor of 18, the same reading can look very different depending on the unit it is written in. A number that looks far from a target may simply be written in the other unit.
Sources
- American Diabetes Association, Diabetes Related Common Terms (entries for mg/dL and mmol/L).
- Diabetes Canada, Checking Blood Sugar.
- American Diabetes Association, New Recommendations for Time-in-Range Targets During Continuous Glucose Monitoring Presented Today at the ADA's Scientific Sessions (press release, June 8, 2019).
- American Diabetes Association, Check Your Blood Glucose.
- Battelino T, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care, 2019;42(8):1593–1603.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Diabetes Tests & Diagnosis.
We made Steadion, an iPhone tracker for people with diabetes or prediabetes. It lets you choose mg/dL or mmol/L, so your numbers appear in the unit you use. Learn more at steadion.fit.