What is the difference between mg/dL and mmol/L?

mg/dL measures the weight of a substance in a deciliter of blood, while mmol/L counts its particles in a liter. They describe the same thing on different scales, so the numbers look different.

Why do US lab reports use different units from other countries?

Most US labs use conventional units such as mg/dL, while most other countries use SI units such as mmol/L. Both are correct; they are just different systems.

How do I convert glucose from mg/dL to mmol/L?

Divide the mg/dL number by about 18. Use this only to understand a report, and read results against the range printed on the report itself.

Are mEq/L and mmol/L the same?

For sodium, potassium, chloride and bicarbonate, yes, the numbers are the same. For some other substances they differ.

Lab units explained: mg/dL, mmol/L and more, US vs other countries

November 6, 2026 · 5 min read · Vita Health Coach

The short answer

A lab unit tells you how a result was measured, such as mg/dL (milligrams per deciliter) or mmol/L (millimoles per liter). US labs mostly use conventional units like mg/dL, while most other countries use SI units like mmol/L, so the same result can look very different. Always read a result with the unit and reference range printed next to it.

What a lab unit tells you

A number on a lab report means nothing without its unit. The unit says what was counted and in how much blood. For example, mg/dL means milligrams of a substance in each deciliter of blood. A deciliter is one tenth of a liter.

Two reports can measure the same thing in different units. A glucose result might read 90 on a US report and 5 on a report from another country, and both can describe the same blood sugar level. The numbers differ only because the units differ.

This is why the unit should always travel with the number. If you write a result down, or read it to a doctor over the phone, include the unit. A number without its unit is easy to misread.

Common units on a blood test report

These are the units you are most likely to see, with plain meanings. You do not need to learn them all. The point is to notice the unit, and to compare a result only with a range in the same unit.

Enzyme results in U/L are especially hard to compare between labs, because the number depends a lot on the method the lab uses.

mg/dL: milligrams per deciliter, a weight of substance in a small amount of blood. Common in the US for glucose, cholesterol, creatinine and BUN.
g/dL: grams per deciliter, used in the US for hemoglobin and albumin.
mmol/L: millimoles per liter, which counts particles rather than weight. Used worldwide for sodium and potassium, and outside the US for glucose and cholesterol.
mEq/L: milliequivalents per liter, used in some US reports for electrolytes. For sodium, potassium, chloride and bicarbonate, mEq/L and mmol/L give the same number.
µmol/L: micromoles per liter, used outside the US for creatinine and bilirubin.
U/L or IU/L: units per liter, used for enzymes such as ALT, AST and ALP.
ng/mL and pg/mL: nanograms and picograms per milliliter, very small amounts, used for tests such as vitamin D, ferritin and vitamin B12.
mIU/L: milli-international units per liter, often used for TSH, a thyroid test.
Percent (%): used for hematocrit and, in the US, for HbA1c.
Cells per microliter, often written x10^3/µL or K/µL: used for white cells and platelets.
fL and pg: femtoliters and picograms, used for the size and hemoglobin content of red cells (MCV and MCH).

US units vs units in other countries

Most US labs use what are called conventional units, such as mg/dL. Most other countries use SI units, short for the International System of Units, such as mmol/L and µmol/L. This matters if a parent has records from abroad, moves between countries, or reads guidance written for another country.

Some results are the same in both systems. White cells and platelets reported as x10^3/µL in the US give the same number as x10^9/L used elsewhere. Sodium and potassium in mEq/L and mmol/L also match.

Some reports show results in both units for certain tests. If you see two numbers for one test, check which one matches the reference range printed beside it.

Others are very different. Here are a few examples of how the numbers relate. They are for understanding only.

Glucose: the mmol/L number is about the mg/dL number divided by 18. So 90 mg/dL is about 5 mmol/L.
Creatinine: the µmol/L number is about the mg/dL number times 88.4. So 1.0 mg/dL is about 88 µmol/L.
Hemoglobin: g/L is the g/dL number times 10. So 13 g/dL is 130 g/L.
Vitamin D: the nmol/L number is about the ng/mL number times 2.5.
HbA1c: the US uses percent; many other countries use mmol/mol, which looks like a much larger number.

Why you should not convert results yourself for decisions

Converting by hand is easy to get wrong, and a slip in the factor can make a normal result look alarming or an abnormal one look fine. Reference ranges also differ between labs, not only because of units but because of methods.

Rounding adds another layer of error. Converted numbers in tables online are often rounded, and small differences can matter for results near the edge of a range.

Use the conversions above to understand a report, not to decide anything. Read each result against the range printed on its own report, in its own units, and ask the doctor to compare results from different countries or labs.

Records from more than one country

If a parent has results from abroad, keep the original reports and note the country and lab for each. When you share them with a US doctor, say clearly that the units may be different. Many doctors are used to this, but it helps to point it out.

If a report is in another language, the test names are often the hardest part. The unit and the range can help you work out which test a line refers to, but ask the doctor to confirm.

When tracking a trend, compare results in the same unit. Mixing mg/dL and mmol/L on one list can make a steady value look like a sudden jump. If anything on a report worries you, ask the doctor, and for urgent symptoms such as chest pain, trouble breathing or signs of a stroke, call 911.

How Vita Health Coach helps

Vita Health Coach reads the result, unit and reference range from a photo of a lab report or from a connected US hospital, and saves them in that person’s own file. Each new result is explained in plain words and compared with the last one. You can ask follow-up questions by voice or text in 28 languages, which helps families who read health information in more than one language. Vita explains health information and never diagnoses or prescribes.

Questions people ask

What is the difference between mg/dL and mmol/L?: mg/dL measures the weight of a substance in a deciliter of blood, while mmol/L counts its particles in a liter. They describe the same thing on different scales, so the numbers look different.
Why do US lab reports use different units from other countries?: Most US labs use conventional units such as mg/dL, while most other countries use SI units such as mmol/L. Both are correct; they are just different systems.
How do I convert glucose from mg/dL to mmol/L?: Divide the mg/dL number by about 18. Use this only to understand a report, and read results against the range printed on the report itself.
Are mEq/L and mmol/L the same?: For sodium, potassium, chloride and bicarbonate, yes, the numbers are the same. For some other substances they differ.

Sources

Vita Health Coach is an iPhone app that keeps a parent’s hospital results in their own file and explains each new one in plain words. Free to try; paid plans in the App Store.

Vita Health Coach on the App Store

General health information, not medical advice. Vita Health Coach explains; it never diagnoses. In an emergency, call 911 or your local emergency number. Read the medical disclaimer.