mg/dL to mmol/L: Understanding Blood Glucose Units
Blood glucose (blood sugar) is reported in two different units depending on where you are in the world. The United States and a handful of other countries use mg/dL (milligrams per deciliter), a mass-based unit. Most of the rest of the world — including the UK, Canada, and much of Europe — uses mmol/L (millimoles per liter), which measures the molar concentration of glucose instead of its weight.
Because the same blood sugar level looks like a completely different number depending on the unit, converting between mg/dL and mmol/L is something people with diabetes, caregivers, and healthcare providers run into often — whether you're reading a glucose meter from a different country, comparing lab results, or just trying to understand a number your doctor mentioned in a different unit.
You'll typically need to convert glucose units when:
- Traveling or relocating: Your glucose meter or local lab may report in a different unit than you're used to
- Reading international guidelines: Medical literature and diabetes associations from different countries often use different units
- Comparing lab reports: Older results or reports from a different healthcare system may use the unit you're not familiar with
- Understanding a doctor's explanation: Clinicians sometimes reference both units when discussing targets
The calculator above converts instantly between the two units. For related health tools, explore our full range of medical calculators.
The Glucose Conversion Formula
Converting mg/dL to mmol/L:
mmol/L = mg/dL ÷ 18
Converting mmol/L to mg/dL:
mg/dL = mmol/L × 18
The precise conversion factor is 18.0182, based on the molecular weight of glucose. Most everyday conversions round this to 18, which is accurate enough for practical use; some clinical references use 18.016 or 18.018 for extra precision.
Worked Example
Say your glucose meter shows 126 mg/dL and you want to know the equivalent in mmol/L:
- Take the mg/dL value: 126
- Divide by 18: 126 ÷ 18 = 7.0
- Result: 7.0 mmol/L
Going the other way, if a lab report shows 5.5 mmol/L:
- Take the mmol/L value: 5.5
- Multiply by 18: 5.5 × 18 = 99
- Result: 99 mg/dL
Blood Glucose Range Reference (mg/dL and mmol/L)
| Category | mg/dL | mmol/L |
|---|---|---|
| Low (hypoglycemia) | Below 70 | Below 3.9 |
| Normal fasting | 70 – 99 | 3.9 – 5.5 |
| Prediabetes (fasting) | 100 – 125 | 5.6 – 6.9 |
| Diabetes range (fasting) | 126 or above | 7.0 or above |
| Normal, up to 2 hrs after eating | Below 140 | Below 7.8 |
These are general reference ranges based on commonly cited fasting glucose criteria. Your own target range may differ based on age, pregnancy status, and existing conditions — always confirm your personal targets with your doctor.
Why Do Countries Use Different Units?
mg/dL measures glucose by weight — how many milligrams of glucose are present in one deciliter of blood. It's the standard in the United States and a few other countries.
mmol/L measures glucose by molar concentration — the actual number of glucose molecules present in one liter of blood. This is the SI (International System of Units) standard, and it's what most countries, including the UK, Canada, Australia, and much of Europe, use on lab reports and glucose meters.
Neither unit is "more correct" than the other — they're just different ways of expressing the same underlying measurement, similar to how temperature can be expressed in Fahrenheit or Celsius.
Glucose Units and A1C
Alongside day-to-day glucose readings, many people with diabetes also track their A1C (HbA1c), a lab test reflecting average blood sugar over the past 2–3 months, reported as a percentage rather than in mg/dL or mmol/L. A1C isn't converted using the same formula as a single glucose reading — it uses a separate estimated average glucose (eAG) formula. If your doctor has given you an A1C-based target, it's worth asking them to translate it into the glucose unit you're most comfortable working with.
Common Mistakes When Reading Glucose Units
Mixing up the two units is one of the most common sources of confusion when people switch glucose meters, travel internationally, or read a foreign lab report. A reading of "5.5" could mean a healthy fasting glucose (5.5 mmol/L) or a dangerously low one if misread as 5.5 mg/dL. Always double-check which unit your device or report is using before interpreting a number — especially if the value looks unusually high or low for the context.
How This Calculator Works
This calculator applies the standard glucose conversion factor (divide by 18 to go from mg/dL to mmol/L, multiply by 18 to go the other way) directly to the number you enter. It performs simple arithmetic only — it doesn't access your medical records, meter history, or any personal data, and it doesn't replace your glucose meter or lab results.
Reference Sources
| Source | Relevance |
|---|---|
| American Diabetes Association (ADA) Standards of Care | Fasting and postprandial glucose target ranges |
| International Federation of Clinical Chemistry (IFCC) | SI unit standards for laboratory reporting, including mmol/L |
| NHS (United Kingdom) | mmol/L-based glucose reference ranges commonly used in the UK |
Using This Tool: This calculator is meant to help you quickly translate a glucose number between units so you can compare it with a reference range or discuss it with your doctor — not to diagnose or manage diabetes on its own. For related tracking tools, see our insulin dose calculator.
Frequently Asked Questions
Divide the mg/dL value by 18. For example, 180 mg/dL ÷ 18 = 10.0 mmol/L. This is the standard conversion factor used for blood glucose.
Multiply the mmol/L value by 18. For example, 7.0 mmol/L × 18 = 126 mg/dL.
A normal fasting blood glucose is generally considered to be between 3.9 and 5.5 mmol/L (70–99 mg/dL). After eating, levels below 7.8 mmol/L (140 mg/dL) at the two-hour mark are generally considered within a normal range for people without diabetes.
It largely comes down to historical convention. The US, along with a few other countries, adopted mass-based reporting (mg/dL) early on, while most of the world adopted the SI molar standard (mmol/L) as part of broader international standardization of laboratory units. Both express the same underlying measurement.
No. This calculator only converts a number you already have from one unit to another. It doesn't measure your blood sugar and isn't a substitute for a glucose meter, lab test, or your doctor's guidance.
The precise molecular-weight-based factor is 18.0182, sometimes rounded to 18.016 or 18.018 in clinical references. For everyday use and mental math, rounding to 18 is accurate enough — the difference is negligible at typical glucose values.
