LDL calculator: three published equations side by side
For healthcare professionals and students. Check results against your local protocols and clinical judgement; this tool does not give medical advice.
This LDL calculator estimates low-density lipoprotein cholesterol (LDL-C) from a standard lipid panel — total cholesterol, HDL cholesterol and triglycerides — using the three equations laboratories actually report: Friedewald (1972), Martin/Hopkins (2013, with its 180-cell factor table) and Sampson/NIH equation 2 (2020). Enter values in mg/dL or mmol/L; switching units converts them for you, and every result is shown in both.
Seeing the three side by side explains why two reports of the same blood can differ, especially when triglycerides are high or LDL-C is low. Each equation’s validity limit is applied, and the Martin/Hopkins cell used is highlighted in the full factor table.
How to use the LDL Cholesterol Calculator
- Choose mg/dL or mmol/L.
- Enter total cholesterol, HDL cholesterol and triglycerides from the same sample.
- Read the three calculated LDL-C values and the non-HDL cholesterol under them.
- Check the warnings: an equation shows “—” when triglycerides are outside its validity range.
- Open the Martin/Hopkins factor table to see which cell was used, and copy the result with its working.
LDL Cholesterol Calculator features
Three equations
Friedewald, Martin/Hopkins and Sampson computed at once from the same inputs.
Complete factor table
All 180 Martin/Hopkins factors, checked against two independent copies, with the cell in use highlighted.
mg/dL and mmol/L
Cholesterol 1 mmol/L = 38.67 mg/dL; triglycerides 1 mmol/L = 88.57 mg/dL.
Validity limits built in
Friedewald is withheld at TG ≥ 400 mg/dL and Sampson above 800 mg/dL, with an explanation.
Working shown
Each equation is written out with your numbers for teaching and checking.
The three LDL equations
The factor table was transcribed from the LDLcalc R package (CRAN archive, version 2.1) and cross-checked cell by cell against the MSD Manual professional Martin equation calculator on 19 October 2026; both match the published strata. Triglyceride and non-HDL values are rounded to whole mg/dL to choose the cell, because the published strata are whole numbers.
- Friedewald: LDL-C = TC − HDL-C − TG ÷ 5 (mg/dL). TG ÷ 5 estimates VLDL cholesterol. Not used when TG ≥ 400 mg/dL. In mmol/L the usual published form is TG ÷ 2.2, which this tool uses when you work in mmol/L. Source: Friedewald WT, Levy RI, Fredrickson DS. Clin Chem 1972;18(6):499–502.
- Martin/Hopkins: LDL-C = non-HDL-C − TG ÷ factor, where the factor (3.1 to 11.9) is read from a table of 30 triglyceride by 6 non-HDL-C strata derived from 1.35 million lipid profiles. Source: Martin SS, Blaha MJ, Elshazly MB, et al. JAMA 2013;310(19):2061–2068.
- Sampson (NIH equation 2): LDL-C = TC/0.948 − HDL-C/0.971 − (TG/8.56 + TG × non-HDL-C/2140 − TG²/16100) − 9.44 (mg/dL), derived against β-quantification for triglycerides up to 800 mg/dL. Source: Sampson M, Ling C, Sun Q, et al. JAMA Cardiol 2020;5(5):540–548.
Worked example
Total cholesterol 200, HDL-C 50 and triglycerides 150 mg/dL (5.17, 1.29 and 1.69 mmol/L) give non-HDL-C 150 mg/dL.
| Equation | Working | LDL-C |
|---|---|---|
| Friedewald | 200 − 50 − 150 ÷ 5 | 120 mg/dL (3.10 mmol/L) |
| Martin/Hopkins | factor 5.7 (TG 147–154, non-HDL 130–159): 150 − 150 ÷ 5.7 | 124 mg/dL (3.20 mmol/L) |
| Sampson | 210.97 − 51.49 − (17.52 + 10.51 − 1.40) − 9.44 | 123 mg/dL (3.19 mmol/L) |
When calculated LDL is not enough
All three are estimates. Calculated LDL-C becomes less reliable at very high triglycerides, with chylomicrons or dysbetalipoproteinaemia (type III), and at low LDL-C levels, where Sampson et al. (2020) note that calculation is less accurate. Above 800 mg/dL (9.0 mmol/L) of triglycerides none of these equations is designed to be used, and a directly measured LDL-C is needed. Non-HDL cholesterol needs no estimation at all and is shown for reference.
LDL Cholesterol Calculator FAQ
How do I calculate LDL cholesterol?
With the Friedewald equation, subtract HDL cholesterol and one fifth of the triglycerides from total cholesterol (all in mg/dL). This LDL calculator also gives the Martin/Hopkins and Sampson estimates, which are usually closer to measured LDL-C when triglycerides are high.
How do I use the LDL calculator with mmol/L?
Choose mmol/L before typing, or switch after — the values are converted with 38.67 mg/dL per mmol/L for cholesterol and 88.57 for triglycerides. In mmol/L, Friedewald uses TG ÷ 2.2.
Why don’t the three equations agree?
They estimate VLDL cholesterol differently. Friedewald assumes a fixed TG:VLDL ratio of 5; Martin/Hopkins varies it with triglycerides and non-HDL-C; Sampson uses a regression including a TG² term. Differences are largest with high triglycerides and low LDL-C.
Why is Friedewald blank?
Friedewald is not used when triglycerides are 400 mg/dL (4.5 mmol/L) or higher. Martin/Hopkins is shown with a warning above that level, and Sampson up to 800 mg/dL.
Does the sample need to be fasting?
Fasting status affects triglycerides and so every calculated LDL-C. Follow your laboratory’s and guideline’s advice; the equations themselves do not change.
What is non-HDL cholesterol?
Total cholesterol minus HDL cholesterol. It includes LDL, VLDL and other atherogenic particles and is shown under the results.