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LDL Cholesterol Calculator (Friedewald Formula)

Estimate Low-Density Lipoprotein (LDL) using the standard Friedewald equation. Supports mg/dL and mmol/L units with built-in validation for high triglyceride levels.

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About

Direct measurement of Low-Density Lipoprotein (LDL) via ultracentrifugation is expensive and time-consuming. Consequently, most clinical laboratories estimate LDL using the Friedewald formula. This method calculates LDL based on three primary lipid panel components: Total Cholesterol, HDL, and Triglycerides. While widely used, the formula possesses a critical limitation: accuracy degrades significantly when Triglyceride levels are elevated.

This tool strictly implements the clinical standards for estimation. It automatically adjusts the division factor based on the selected unit of measurement (mass vs. molar). It also includes a safety check for Triglycerides exceeding 400 mg/dL (4.5 mmol/L), a scenario where the Friedewald equation becomes mathematically invalid and direct measurement is required.

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Formulas

The calculator uses the Friedewald Equation. The Very Low-Density Lipoprotein (VLDL) is estimated as a fixed fraction of Triglycerides.

{
LDL = TC - HDL - TG5 (for mg/dL)LDL = TC - HDL - TG2.17 (for mmol/L)

Note: This formula assumes the ratio of mass of triglycerides to cholesterol in VLDL is constant.

Reference Data

Lipid ComponentOptimal Range (mg/dL)Optimal Range (mmol/L)Role in Formula
Total Cholesterol< 200< 5.17Base Value (TC)
HDL (Good)≥ 60≥ 1.55Subtracted Factor
Triglycerides< 150< 1.70Used to estimate VLDL (TG/5)
LDL (Calculated)< 100< 2.60Result

Frequently Asked Questions

The formula relies on the assumption that VLDL cholesterol is one-fifth of the triglyceride level. This relationship breaks down if Triglycerides exceed 400 mg/dL (4.5 mmol/L) or if the patient has Type III hyperlipoproteinemia (dysbetalipoproteinemia). In these cases, a Direct LDL test is necessary.
This factor estimates the VLDL (Very Low-Density Lipoprotein) cholesterol. In a standard fasting state, the mass ratio of Triglycerides to Cholesterol in VLDL particles is approximately 5:1. Subtracting HDL and VLDL from the Total Cholesterol leaves the LDL fraction.
Yes. Triglyceride levels spike significantly after eating (postprandial state). Since the Friedewald formula relies heavily on the Triglyceride value to estimate VLDL, using non-fasting numbers will falsely lower the calculated LDL result.
For Cholesterol (Total, HDL, LDL), 1 mmol/L = 38.67 mg/dL. For Triglycerides, the molecular weight is different, so 1 mmol/L = 88.57 mg/dL.