HDL Cholesterol — mmol/L to mg/dL

In short To convert HDL cholesterol from mmol/L to mg/dL, multiply by 38.6654 — so one mmol/L is 38.6654 mg/dL, and one mg/dL is 0.0258629 mmol/L. 40 mg/dL is 1.0 mmol/L; 50 mg/dL is 1.3 mmol/L; 60 mg/dL is 1.6 mmol/L. The factor comes from the molar mass, because cholesterol has a molar mass of 386.65 g/mol, and HDL measures the same molecule; that is why it differs for every analyte and why a single "lab unit converter" factor does not exist. HDL uses the same factor as total cholesterol because it is the same molecule — what differs is the lipoprotein carrying it, not the substance being counted. That is also why the numbers are small: HDL is typically around a quarter of the total, so the SI figure often lands near 1 and is easy to mistake for a different scale entirely. This converts units. It does not interpret results, does not compare your value against a reference interval, and is not a substitute for the clinician who ordered the test — reference intervals differ between laboratories, methods and populations.