Cholesterol mg/dL to mmol/L: how to convert your lipid units

Your report says LDL 100 mg/dL while a guideline quotes 2.6 mmol/L. Those are the same result in two units, and one division translates between them.

Use our LDL calculator to enter your lipid panel in either unit, then try our cholesterol ratio calculator to check total/HDL without converting anything twice.

Why cholesterol has two unit systems

United States laboratories report cholesterol in milligrams per deciliter, written mg/dL. Laboratories in the UK and many other countries report millimoles per liter, written mmol/L. The AHA describes levels in mg/dL, while the NHS presents its cholesterol guidance in mmol/L, so you will meet both if you read across countries.

mg/dL measures mass in a volume of blood. mmol/L counts molecules in a volume of blood. Moving between them requires the weight of the molecule involved. Cholesterol and triglycerides weigh different amounts, so each needs its own factor. That single fact explains most conversion errors.

How to convert cholesterol units

The same factor covers total cholesterol, LDL, HDL, and non-HDL, because all of them are cholesterol.

cholesterol in mmol/L ≈ cholesterol in mg/dL ÷ 38.67

To go back, multiply instead of dividing.

cholesterol in mg/dL ≈ cholesterol in mmol/L × 38.67

Convert each cholesterol value before you subtract or compare. Keep extra digits during the arithmetic and round once at the end, to one decimal place in mmol/L the way most reports print it.

Why triglycerides need their own factor

Triglycerides are heavier molecules, so their divisor is larger.

triglycerides in mmol/L ≈ triglycerides in mg/dL ÷ 88.57

Reverse it with multiplication.

triglycerides in mg/dL ≈ triglycerides in mmol/L × 88.57

Never convert a triglyceride value with 38.67, and never convert a cholesterol value with 88.57. Read the line on your report before you pick a divisor.

Worked cholesterol conversion example

Take LDL cholesterol of 100 mg/dL. Divide by the cholesterol factor: 100 ÷ 38.67 = 2.586, which rounds to about 2.6 mmol/L.

Reverse the trip to check your work: 2.6 × 38.67 = 100.5, which rounds back to about 100 mg/dL. The small gap comes from rounding 2.586 to 2.6, not from an error in the factor.

For contrast inside the same panel, convert triglycerides of 150 mg/dL with their own divisor: 150 ÷ 88.57 = 1.694, or about 1.7 mmol/L. One panel, two divisors, no shared shortcut.

Why cholesterol ratios ignore units

A ratio divides one cholesterol value by another. When both use the same unit, the units cancel and the answer has no unit at all.

LDL 120 with HDL 50 gives 120 ÷ 50 = 2.4. In mmol/L that is about 3.1 ÷ 1.3, which still equals about 2.4. Convert both inputs or convert neither. What breaks the ratio is mixing units, such as dividing an mg/dL LDL by an mmol/L HDL. The same rule covers subtraction: compute non-HDL from total and HDL in one shared unit.

Do not use glucose math for cholesterol

Blood glucose converts with divide by 18. Cholesterol does not.

Glucose is a lighter molecule, so its factor is smaller. Applying divide by 18 to an LDL of 100 mg/dL would claim about 5.6 mmol/L, nearly double the correct 2.6. That error can make a normal result look alarming or a high result look ordinary.

If you track both conditions, keep the tools apart. Use our blood sugar converter for glucose readings only, where divide by 18 belongs. Use the lipid calculators above for cholesterol, where 38.67 belongs.

Common unit mistakes

• Typing an mg/dL number into a field set to mmol/L, or the reverse. Check the unit selector before you type.
• Converting total cholesterol but forgetting HDL, then subtracting across units for non-HDL.
• Converting a ratio itself. Convert the two inputs or leave the ratio alone.
• Borrowing the glucose factor of 18, or the triglyceride factor of 88.57, for a cholesterol value.
• Rounding after every step. Round once at the end so small errors do not stack.

Limitations of unit conversion

Conversion restates a number. It does not improve the original measurement.

A converted LDL carries every limitation of the original measurement. If the LDL was calculated from triglycerides rather than measured directly, the estimate stays an estimate in both units. High triglycerides, nonfasting samples, and unusual lipid patterns affect the value before conversion ever touches it.

Conversion also cannot bridge methods. Two laboratories can report slightly different numbers for the same blood sample because their assays differ. Matching the units lets you compare the reports side by side, but it does not erase method differences.

Treat a converted value near a treatment threshold with care. Confirm which unit your clinician uses, bring the original report, and ask before you act on a number you translated yourself. Do not stop or change prescribed medicine based on arithmetic. When your units match your report, run them through our LDL calculator and cholesterol ratio calculator for a clean same-unit check.