Blood glucose is measured in two main units: milligrams per deciliter (mg/dL), used in the United States, and millimoles per liter (mmol/L), used in most of the rest of the world. Both describe the same concentration of glucose. To convert, divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to get mg/dL.
Why Two Different Units Exist
The US retained traditional mass-based units (mg/dL) for most clinical lab results, while the rest of the world adopted the International System of Units (SI), which uses molar concentration (mmol/L). A molecule of glucose has a molar mass of 180 g/mol, so 1 mmol/L equals 18 mg/dL, making the conversion factor 18.
Quick Conversion Formulas
- mg/dL to mmol/L: mg/dL / 18 = mmol/L
- mmol/L to mg/dL: mmol/L x 18 = mg/dL
Examples:
- 100 mg/dL / 18 = 5.6 mmol/L
- 126 mg/dL / 18 = 7.0 mmol/L
- 7.8 mmol/L x 18 = 140 mg/dL
- 11.1 mmol/L x 18 = 200 mg/dL
Master Conversion Chart
| mg/dL | mmol/L | Clinical Meaning |
|---|---|---|
| 70 | 3.9 | Lower end of normal (hypoglycemia threshold) |
| 90 | 5.0 | Normal fasting |
| 100 | 5.6 | Upper normal fasting / lower prediabetes |
| 110 | 6.1 | Prediabetes (fasting) |
| 126 | 7.0 | Diabetes threshold (fasting) |
| 140 | 7.8 | Upper normal 2-hour post-meal |
| 180 | 10.0 | Typical target ceiling post-meal in diabetes |
| 200 | 11.1 | Diabetes (2-hour OGTT or random with symptoms) |
| 250 | 13.9 | Significantly elevated |
| 300 | 16.7 | High; risk of complications |
| 400 | 22.2 | Severe hyperglycemia; urgent care |
Diagnostic Cutoffs in Both Units
Diagnostic thresholds from the American Diabetes Association and World Health Organization:
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose | < 100 mg/dL (< 5.6 mmol/L) | 100-125 mg/dL (5.6-6.9 mmol/L) | ≥ 126 mg/dL (≥ 7.0 mmol/L) |
| 2-hr OGTT | < 140 mg/dL (< 7.8 mmol/L) | 140-199 mg/dL (7.8-11.0 mmol/L) | ≥ 200 mg/dL (≥ 11.1 mmol/L) |
| Random glucose + symptoms | N/A | N/A | ≥ 200 mg/dL (≥ 11.1 mmol/L) |
| A1C | < 5.7% | 5.7-6.4% | ≥ 6.5% |
For more on how A1C relates to these numbers, see our A1C levels guide.
A1C Reporting: Percentage vs mmol/mol
A1C itself has two reporting conventions:
- DCCT/NGSP (percentage): Standard in the US and most English-speaking countries
- IFCC (mmol/mol): Used in many European countries
Conversion: mmol/mol = (A1C percent x 10.93) – 23.5
| A1C (%) | A1C (mmol/mol) |
|---|---|
| 5.0 | 31 |
| 5.7 | 39 |
| 6.5 | 48 |
| 7.0 | 53 |
| 8.0 | 64 |
| 10.0 | 86 |
Why Getting the Units Right Matters
Mixing up units can lead to dangerous misinterpretation. Imagine reading “glucose 7” – in mmol/L that means 126 mg/dL (diabetic fasting range), but in mg/dL it would be critically low. Common pitfalls:
- Traveling internationally with a glucometer that switched modes
- Downloading apps configured for the other region
- Reading lab results from a different country
- Medication instructions that specify only one unit
How to Check Your Meter’s Units
- Look at the reading display – most meters show “mg/dL” or “mmol/L” after the number
- Check the instruction manual for the default unit
- Sanity check: fasting values between 70-100 are almost always mg/dL; values between 4-6 are almost always mmol/L
- If your meter switched accidentally, most models allow changing units in settings
According to the CDC, US clinical testing defaults to mg/dL unless otherwise specified.
Converting for Food Logs and CGMs
Most continuous glucose monitors let you toggle between units. If you track data in apps or share logs internationally, be explicit about units in every entry. For deeper context on what different numbers mean, visit our prediabetes hub.
The Bottom Line
Blood glucose units are simply two ways of describing the same quantity. Divide by 18 to convert mg/dL to mmol/L, or multiply by 18 to go the other direction. Know which unit your meter, lab, and clinician use, and keep a printed conversion chart handy when traveling or comparing records across regions. The numbers only mean something when you know which scale you are reading.
