Blood Glucose Calculator
Blood glucose is reported in two different units around the world: milligrams per deciliter (mg/dL), used in the United States, and millimoles per liter (mmol/L), used in most other countries. If you travel, read international health articles, or use a meter with different settings, you need to convert between them quickly. The blood glucose calculator above does exactly that — enter a value in either unit and it instantly shows you the equivalent in the other, so a reading is never a mystery again.
How to Use This Calculator
1. Enter your blood glucose value as a number, for example 100 or 5.5.
2. Choose the unit of the value you entered from the dropdown: mg/dL or mmol/L.
3. Click Calculate. The tool divides by 18 to go from mg/dL to mmol/L, or multiplies by 18 to go the other way, and displays both values side by side.
4. Click Reset to clear the form and convert another reading.
Worked Example
Suppose your meter reads 100 mg/dL and you want to know what that is in mmol/L, the unit your doctor's international guidelines use:
- 100 ÷ 18 = 5.6 mmol/L (rounded to one decimal)
Now the reverse: a friend in the UK tells you their reading was 5.5 mmol/L.
- 5.5 × 18 = 99 mg/dL
Both directions take a single click in the calculator. Try your own numbers — for instance, 126 mg/dL (the fasting diabetes threshold) converts to 7.0 mmol/L, and 200 mg/dL converts to 11.1 mmol/L.
More Helpful Information
Why two units exist
The mg/dL unit measures the mass of glucose in a volume of blood, while mmol/L measures the number of glucose molecules. The US held onto mg/dL for historical reasons; most of the rest of the world standardized on the SI unit mmol/L. Neither is more "correct" — they describe the same thing, just with different scales.
The magic number 18
The conversion factor comes from the molecular weight of glucose (about 180 g/mol). One mmol/L equals 18.018 mg/dL, which is rounded to 18 for everyday use. That is why the math is so simple: divide mg/dL by 18, or multiply mmol/L by 18.
Common reference points
Memorizing a few anchor values helps you interpret readings in either unit: 70 mg/dL = 3.9 mmol/L (low blood sugar threshold), 100 mg/dL = 5.6 mmol/L (top of normal fasting), 126 mg/dL = 7.0 mmol/L (fasting diabetes threshold), 140 mg/dL = 7.8 mmol/L, and 200 mg/dL = 11.1 mmol/L. With these landmarks, any converted value makes intuitive sense.
Mistakes to avoid
The most dangerous mistake is acting on a number in the wrong unit — treating 5.5 mmol/L as if it were 5.5 mg/dL, for example, would suggest impossibly low blood sugar. Always check which unit your meter displays, especially after traveling or replacing a device, since some meters let you switch units in the settings.
Tips for travelers with diabetes
Before a trip, set your meter or CGM app to the unit used at your destination, or keep this converter bookmarked on your phone. Carry a small card with your target range written in both units so any doctor, anywhere, understands your numbers instantly.
Frequently Asked Questions
1. How do I convert mg/dL to mmol/L?
Divide the mg/dL value by 18. For example, 180 mg/dL ÷ 18 = 10 mmol/L.
2. How do I convert mmol/L to mg/dL?
Multiply the mmol/L value by 18. For example, 6 mmol/L × 18 = 108 mg/dL.
3. Which countries use mmol/L?
Most countries outside the United States, including the UK, Canada, Australia, and EU nations, use mmol/L for blood glucose.
4. What is a normal blood sugar in mmol/L?
Fasting normal is roughly 3.9–5.5 mmol/L (70–99 mg/dL); under 7.8 mmol/L (140 mg/dL) two hours after meals.
5. What does 7.0 mmol/L mean in mg/dL?
It equals 126 mg/dL — the fasting threshold used in diabetes diagnosis.
6. Is 10 mmol/L high blood sugar?
Yes, 10 mmol/L (180 mg/dL) is above target for most people and indicates hyperglycemia worth addressing.
7. Why is the conversion factor 18?
It comes from glucose's molecular weight of about 180 g/mol, making 1 mmol/L equal to roughly 18 mg/dL.
8. Can my glucose meter show both units?
Many meters let you switch units in the settings menu, but some are locked to the unit of the country where they were sold.
9. What is 5.5 mmol/L in mg/dL?
99 mg/dL — right at the top of the normal fasting range.
10. Does the conversion work for A1C too?
No. A1C uses its own conversion between % and mmol/mol, which is different from the glucose unit conversion.
11. What is considered low blood sugar in both units?
Below 70 mg/dL, which is below 3.9 mmol/L, is generally considered hypoglycemia.
12. Are the converted values exact?
They are rounded for readability. The exact factor is 18.018, but 18 is the standard used in clinical practice.
13. Why do research papers use mmol/L?
Scientific literature follows SI units, so studies and international guidelines report glucose in mmol/L.
14. How can I quickly estimate without a calculator?
Divide mg/dL by 20 for a rough answer, then add about 10% — or just bookmark this converter for exact results.
15. Should I worry if my meter switched units?
Do not panic — just convert your readings with this tool and change the meter setting back. Never dose insulin based on a misread unit.
CONCLUSION
Converting blood glucose between mg/dL and mmol/L is simple math, but getting it right matters — especially when medication decisions depend on the number. With this blood glucose calculator, the answer is always one click away. Bookmark it, use it when reading international guidelines or traveling, and always double-check your meter's unit setting. Clear numbers lead to confident, safe diabetes management.