Blood Sugar Units Converter (mg/dL to mmol/L)
Convert blood glucose readings between mg/dL and mmol/L instantly, and see how your fasting value compares to normal, prediabetes and diabetes reference ranges.
Blood Sugar Units Converter (mg/dL ↔ mmol/L)
Blood Sugar Converter Formula
Where:
- \(\text{mg/dL}\) — glucose concentration in milligrams per deciliter (used in the USA and a few other countries)
- \(\text{mmol/L}\) — glucose concentration in millimoles per liter (used in most of the world, including Europe, Canada and Australia)
- \(18.016\) — the conversion factor, derived from the molecular weight of glucose (180.156 g/mol)
The two units describe the same concentration on different scales. Because one mole of glucose weighs 180.156 grams, every 1 mmol/L corresponds to 18.016 mg/dL. In everyday use many people round this to 18.
Blood Sugar Converter – Calculation Example
Example: a fasting glucose meter reading of 95 mg/dL needs to be converted to mmol/L.
\[ \text{mmol/L} = \frac{95}{18.016} = 5.27 \]
Result: 95 mg/dL = 5.27 mmol/L. This value falls inside the normal fasting range of 70–99 mg/dL (3.9–5.5 mmol/L).
How to use the calculator
- Enter your reading in the Glucose value field.
- Choose the unit of your reading — mg/dL or mmol/L — from the Unit dropdown next to the input field.
- Read the result under Your Results: the converted value in the other unit, an interpretation for fasting glucose, and a table of typical reference ranges.
Why two units for blood sugar?
Blood glucose is reported in mg/dL in the United States, Japan and a handful of other countries, while the SI unit mmol/L is standard in the UK, Canada, Australia and most of Europe. The difference matters when reading research articles, comparing meter readings abroad, or discussing results with doctors trained elsewhere — the same measurement can look dramatically different numerically. A normal fasting value of 5 mmol/L, for example, appears as 90 mg/dL, roughly eighteen times larger.
The conversion is not an arbitrary rule of thumb: it follows directly from chemistry. Concentration in mmol/L counts particles (moles), while mg/dL counts mass. Since one mole of glucose weighs 180.156 g, multiplying mmol/L by 18.016 gives mg/dL, and dividing mg/dL by 18.016 returns mmol/L. For quick mental estimates, dividing by 18 is accurate to about 0.1%.
The calculator also places your value on the standard fasting glucose scale used by the American Diabetes Association and the World Health Organization. Keep in mind that these thresholds apply to fasting plasma glucose (measured after at least 8 hours without food). Readings taken after a meal are expected to be higher, and different criteria — such as the HbA1c test or an oral glucose tolerance test — are used for an actual diagnosis.
Interpreting the reference ranges
| Category (fasting) | mg/dL | mmol/L |
|---|---|---|
| Hypoglycemia | below 70 | below 3.9 |
| Normal | 70–99 | 3.9–5.5 |
| Prediabetes | 100–125 | 5.6–6.9 |
| Diabetes | 126 or higher | 7.0 or higher |
A single reading above or below a threshold is not a diagnosis. Blood glucose fluctuates through the day with food, exercise, stress and illness, so doctors rely on repeated measurements and additional tests before drawing conclusions.
Assumptions and limitations
- Fasting thresholds only. The interpretation assumes the reading was taken after at least 8 hours of fasting. Post-meal (postprandial) values are normally higher and should be judged against different targets.
- Plasma vs. whole blood. The reference ranges refer to plasma glucose. Some home glucose meters report whole-blood values, which read roughly 10–12% lower; check your meter's documentation.
- Not medical advice. This tool converts units and compares them to published reference ranges. It cannot diagnose hypoglycemia, prediabetes or diabetes. If a result is unexpected or you feel unwell, consult a healthcare professional.
- Special situations. Targets for pregnant women, children and people already diagnosed with diabetes may differ from the general ranges shown here.
If you often convert between unit systems, you may also find our Fahrenheit to Celsius temperature converter, the fuel economy converter (MPG ↔ L/100 km) and the speed unit converter useful.
Frequently Asked Questions
How do I convert blood sugar by hand without a calculator?
Divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to get mg/dL. This shortcut differs from the exact factor of 18.016 by less than 0.1%, which is far smaller than the accuracy of a home glucose meter. For example, 126 mg/dL ÷ 18 ≈ 7 mmol/L, and 5.5 mmol/L × 18 ≈ 99 mg/dL.
Is 18.016 or 18 the correct conversion factor?
The exact factor is 18.016 (often written as 18.02), because one mole of glucose weighs 180.156 grams and 1 deciliter is 0.1 liter. The number 18 is simply a convenient rounding. For everyday readings both give practically identical results: 100 mg/dL is 5.55 mmol/L with the exact factor and 5.56 with the rounded one.
What is a good blood sugar level after a meal?
The normal and prediabetes ranges shown for fasting values do not apply after eating. In people without diabetes, glucose measured about 2 hours after a meal typically stays below 140 mg/dL (7.8 mmol/L). Values between 140 and 199 mg/dL (7.8–11.0 mmol/L) at that point suggest prediabetes, and 200 mg/dL (11.1 mmol/L) or higher falls in the diabetes range. Targets for people with diabetes are individualized — ask your doctor.
Why does my meter show a different value than my lab report?
Two common reasons: lab results usually measure plasma glucose, while many home meters measure whole blood, which reads roughly 10–12% lower. In addition, meters are allowed a margin of error of up to about ±15%, and readings vary with sample technique, strip quality and timing. Small differences between a meter and a lab draw are normal; large or repeated gaps deserve a conversation with your healthcare provider.
Can I use this converter for HbA1c results?
No. HbA1c is a different measurement — a percentage of glycated hemoglobin reflecting average glucose over roughly 3 months — and it does not convert with the factor 18.016. Some countries report HbA1c in mmol/mol instead of percent; that conversion uses a separate formula (DCCT to IFCC), not the glucose factor. Look for a dedicated HbA1c converter for that task.
Is a single high or low reading a diagnosis of diabetes or hypoglycemia?
No. Blood glucose changes constantly with food, exercise, stress, medication and illness, so diagnostic guidelines require repeated fasting measurements or confirmatory tests such as HbA1c or an oral glucose tolerance test. Use this converter to translate units and get a rough orientation, and discuss any unusual readings or symptoms with a healthcare professional.
What is the most common mistake when converting glucose units?
Mixing up the direction of the conversion: mg/dL values are about 18 times larger than the equivalent mmol/L values, so a reading of 7 must be mmol/L, and a reading of 126 must be mg/dL. If a converted result looks wildly off (for example a "normal" 90 turning into 1600), you divided instead of multiplied. As a sanity check, normal fasting glucose is 70–99 mg/dL or 3.9–5.5 mmol/L.