How LDL Cholesterol Is Calculated (Friedewald)
Most labs estimate LDL rather than measuring it directly, using the Friedewald equation. The triglyceride term approximates VLDL cholesterol:
LDL = Total cholesterol − HDL − (Triglycerides ÷ 5) LDL = Total cholesterol − HDL − (Triglycerides ÷ 2.2) It is quick and free but only an estimate. It is unreliable when triglycerides exceed 400 mg/dL (about 4.5 mmol/L), in non-fasting samples, and at very low LDL. The newer Martin-Hopkins method uses an adjustable factor instead of a fixed ÷5 and is more accurate in those situations; many labs now report it.
Convert LDL Between mmol/L and mg/dL
LDL uses the same factor as total and HDL cholesterol — 38.67. Multiply mmol/L by 38.67 for mg/dL, or divide by 38.67 to reverse. For the whole lipid panel, see the cholesterol conversion calculator.
| mmol/L | mg/dL | Category |
|---|---|---|
| 2.0 mmol/L | 77.3 mg/dL | Optimal |
| 2.59 mmol/L | 100.2 mg/dL | Optimal / near-optimal border |
| 3.0 mmol/L | 116.0 mg/dL | Near optimal |
| 3.4 mmol/L | 131.5 mg/dL | Borderline high |
| 4.1 mmol/L | 158.5 mg/dL | Borderline high |
| 4.9 mmol/L | 189.5 mg/dL | High |
LDL Cholesterol Reference Ranges
| Category | mg/dL | mmol/L |
|---|---|---|
| Optimal | Below 100 mg/dL | Below 2.59 mmol/L |
| Near optimal | 100–129 mg/dL | 2.59–3.34 mmol/L |
| Borderline high | 130–159 mg/dL | 3.36–4.11 mmol/L |
| High | 160–189 mg/dL | 4.14–4.89 mmol/L |
| Very high | 190 mg/dL and above | 4.91 mmol/L and above |
These are general categories. People at higher cardiovascular risk are often given lower LDL targets (for example, below 70 mg/dL / 1.8 mmol/L), which your provider sets based on your overall risk. HDL and triglycerides round out the panel — see the HDL and triglycerides converters.
Worked Example
Total cholesterol 200 mg/dL, HDL 50 mg/dL, triglycerides 150 mg/dL:
LDL = 200 − 50 − (150 ÷ 5) = 120 mg/dL 120 mg/dL is in the near-optimal range. In mmol/L, that LDL is 120 ÷ 38.67 ≈ 3.1 mmol/L.
Frequently Asked Questions
How is LDL calculated?
Friedewald: LDL = total − HDL − (triglycerides ÷ 5) in mg/dL, or ÷ 2.2 in mmol/L.
How do you convert LDL mmol/L to mg/dL?
Multiply by 38.67. For example, 2.59 mmol/L is about 100 mg/dL.
When does the Friedewald estimate fail?
When triglycerides are above 400 mg/dL (4.5 mmol/L), in non-fasting samples, or at very low LDL.
What LDL is optimal?
Below 100 mg/dL (about 2.59 mmol/L), with lower targets for higher-risk people.
References
- MDCalc — Friedewald LDL-C Calculator (equation, units, and limitations).
- LDL cholesterol factor 38.67 (mmol/L ↔ mg/dL); Friedewald TG divisor 5 (mg/dL) or 2.2 (mmol/L) — standard clinical references.
Conclusion
Estimate LDL with the Friedewald equation, or convert an LDL value with the ×38.67 factor. Remember the estimate breaks down at high triglycerides — interpret LDL with your full panel, cardiovascular risk, and provider.