mg/dL vs mmol/L: converting lab units
Updated
Short answer
mg/dL measures mass per volume and mmol/L measures amount of substance per volume, so converting needs a factor that depends on the marker. For total cholesterol 1 mmol/L = 38.67 mg/dL, and for glucose 1 mmol/L = 18.02 mg/dL.
Why two units exist
Mass units such as mg/dL say how many milligrams of a substance are in a decilitre of blood. Molar units such as mmol/L say how many millimoles, a count of molecules, are in a litre. Many countries use SI units in laboratory medicine, which favour mmol/L, while laboratories in the United States mostly report mg/dL. Practice varies by country, by lab and by marker, so read the unit on your own report.
How to convert between them
Going between a mass unit and a molar unit needs the substance's molar mass M, in grams per mole.
mg/dL = mmol/L × M ÷ 10
The ÷ 10 comes from the volumes: 1 mmol/L is M mg per litre, and a litre is 10 decilitres, so it is M ÷ 10 mg/dL. Cholesterol has a molar mass of about 386.65 g/mol, so 1 mmol/L is about 38.67 mg/dL, and 5.0 mmol/L is about 193 mg/dL.
Common conversion factors
| Marker | Conversion | The other way |
|---|---|---|
| Total, LDL, HDL and non-HDL cholesterol | 1 mmol/L = 38.67 mg/dL | 1 mg/dL = 0.02586 mmol/L |
| Triglycerides | 1 mmol/L = 88.57 mg/dL | 1 mg/dL = 0.01129 mmol/L |
| Glucose | 1 mmol/L = 18.02 mg/dL | 1 mg/dL = 0.05551 mmol/L |
| Creatinine | 1 µmol/L = 0.01131 mg/dL | 1 mg/dL = 88.42 µmol/L |
| Urea (as BUN) | 1 mmol/L = 2.801 mg/dL | 1 mg/dL = 0.357 mmol/L |
| Calcium | 1 mmol/L = 4.008 mg/dL | 1 mg/dL = 0.2495 mmol/L |
| Uric acid | 1 µmol/L = 0.01681 mg/dL | 1 mg/dL = 59.48 µmol/L |
Each marker has its own factor because each substance has its own molar mass. Triglycerides, for example, are much heavier molecules than cholesterol, so their factor is larger. See each marker's own page, linked from the marker index, for the units and factors of every marker.
Conversions that are not a simple multiplication
- HbA1c is reported as a percentage (the NGSP or DCCT scale) or in mmol/mol (the IFCC scale). The link between them is a line with an offset, not a multiplication: mmol/mol = (% − 2.15) × 10.929.
- Enzymes such as ALT and AST are reported in U/L (the same number as IU/L) or, less often, in µkat/L. 1 µkat/L is 60 U/L.
- Lipoprotein(a) is reported in mg/dL or nmol/L. There is no reliable factor between them because the particles differ in size, so BiomarkerHQ does not convert it.
- Haemoglobin in mmol/L is not converted, because labs use different molar bases.
Check the unit before you trust a converted number
A converted number is only as reliable as the unit you started with. Read the unit printed on the report, keep the original value, and convert only to compare. The lab unit converter shows the factor it used, so you can check the arithmetic yourself.
Frequently asked questions
How do I convert cholesterol from mmol/L to mg/dL?
Multiply by 38.67. For example, 5.0 mmol/L is about 193 mg/dL. To go the other way, divide by 38.67.
How do I convert glucose from mmol/L to mg/dL?
Multiply by 18.016, which is often rounded to 18. For example, 5.5 mmol/L is about 99.1 mg/dL. To go the other way, divide by 18.016.
Why is the factor for triglycerides different from cholesterol's?
Each marker has its own molar mass, so each has its own factor. Triglycerides are heavier molecules than cholesterol, so 1 mmol/L = 88.57 mg/dL but 1 mmol/L = 38.67 mg/dL.
Does converting units change what a result means?
No. It changes only how the number is written. What a result means depends on the marker, the method and the person, and belongs with a qualified clinician.
Sources
Related
Keep your results in one place
The dashboard works without an account and keeps your data in your browser unless you sign in.