Blood sugar converter: mg/dL and mmol/L
One number in, both units out — and the fasting reference ranges alongside, so the converted figure means something.
Your result
Fasting glucose reference ranges
- Normal — under 100 mg/dL (5.6 mmol/L)
- Prediabetes (ADA) — 100–125 mg/dL (5.6–6.9 mmol/L)
- Diabetes range — 126 mg/dL (7.0 mmol/L) or more
Formula: Molar mass of glucose 180.1559 g/mol (NIST), so 1 mmol/L = 18.0156 mg/dL. ADA’s own tables round the factor to 18, which is why 126 mg/dL pairs with exactly 7.0 mmol/L
Why there are two units at all
Blood sugar is a concentration, and there are two reasonable ways to express one. Milligrams per decilitre states the mass of glucose in a fixed volume of blood. Millimoles per litre states the number of glucose molecules, which is what actually interacts with the rest of your chemistry.
The United States, Germany, Italy, Spain, Poland, Japan and much of Latin America use mg/dL. The United Kingdom, most of Scandinavia, Australia, Canada and China use mmol/L. France is its own case and reports grams per litre, which is mg/dL divided by a hundred. Neither convention is more correct; the split is historical. Anyone reading an international forum, a study, a device manual or a relative's test results will eventually need to convert.
The conversion factor and where it comes from
The factor is not arbitrary. Glucose has a molar mass of 180.1559 grams per mole, and a decilitre is a tenth of a litre; putting those together gives 18.0156 mg/dL for every 1 mmol/L. To go from mg/dL to mmol/L, divide by 18.0156; to go the other way, multiply.
The rough version people use in their heads — divide by 18, or multiply by 18 — is accurate to about a tenth of a percent, which is far inside the error of any home meter. It is also what the ADA's own tables do, which is why its thresholds in the two units line up as exact round pairs rather than as awkward decimals. The calculator uses the precise factor and shows the arithmetic under the result.
Note that this factor is specific to glucose. Other blood analytes have their own, because they have their own molar mass: cholesterol converts at 38.67, triglycerides at 88.57. A single "mg/dL to mmol/L" factor does not exist.
What the converted number means
A conversion on its own is arithmetic. The reference ranges above turn it into information, and they are the American Diabetes Association's fasting plasma glucose categories, printed with their source.
One thing worth knowing before you compare your reading with them: the ADA and the WHO do not agree on where impaired fasting glucose begins. The ADA draws that lower boundary below where the WHO draws it, and both figures are in the source line under the scale. It is not a rounding difference. The WHO looked at the same evidence in 2006 and declined to move, on the grounds that the people the lower boundary adds carry roughly half the risk of going on to develop diabetes. The consequence for you is concrete: a fasting reading in the gap between the two is prediabetes under American criteria and normal under WHO criteria. If your doctor and a website disagree about your result, this is usually why. The two bodies use the same threshold for diabetes itself.
What the ranges do not cover
They are fasting ranges, measured after eight or more hours without food. A reading taken an hour after lunch will be higher in anyone, including people with entirely normal glucose control, and comparing it against a fasting range will frighten you for no reason. There is a separate piece on what a random, non-fasting reading means.
They also apply to venous plasma glucose from a laboratory. Home meters measure capillary blood and most report a plasma-equivalent value, but they carry a permitted error of up to 15 %, which is enough to move a reading across a boundary. Do not diagnose anything from a meter.
And they are adult, non-pregnant ranges. Pregnancy uses different and lower thresholds, set separately for gestational diabetes screening.
Frequently asked questions
How do I convert mg/dL to mmol/L?
Divide by 18.0156. The factor is the molar mass of glucose, 180.1559 g/mol, expressed per decilitre. Dividing by 18 in your head is accurate enough for any practical purpose — and it is what the ADA tables themselves do, which is why 126 mg/dL pairs with exactly 7.0 mmol/L.
How do I convert mmol/L to mg/dL?
Multiply by 18.0156. For example, 5.5 mmol/L is about 99 mg/dL.
What is a normal fasting blood sugar?
The bands above the calculator are the ADA fasting plasma glucose categories in both units. WHO uses a higher lower boundary for impaired fasting glucose, and both are named in the source line.
Does the same factor work for cholesterol or triglycerides?
No. Each substance has its own factor because each has its own molar mass. Cholesterol converts at 38.67 mg/dL per mmol/L, triglycerides at 88.57.
Why does my meter disagree with my lab result?
Home meters are permitted an error of up to about 15 % against a laboratory reference, and they measure capillary rather than venous blood. A difference of 10 to 15 mg/dL between a meter and a lab draw taken at the same moment is within specification.
Read next
Other calculators
- HbA1c to average glucose HbA1c in % or mmol/mol, converted to estimated average glucose in both units.
- HOMA-IR and QUICKI Fasting glucose plus fasting insulin, in either unit, with the bands and their caveats.
- Glycemic load of a meal Add foods and grams, get the GL of the whole plate and its weighted glycemic index.
This calculator is educational and is not a diagnosis. It cannot replace a blood test or a conversation with your doctor. If a result worries you, or if you have symptoms, take the numbers to a clinician rather than acting on them alone.