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LDL Cholesterol Calculator
Your LDL cholesterol by all three equations at once — Friedewald, Martin-Hopkins and Sampson — in mg/dL or mmol/L, with the full comparison chart below.
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Why there are three LDL equations, and why they disagree
A standard lipid panel does not measure LDL cholesterol. It measures total cholesterol, HDL cholesterol and triglycerides; LDL-C is calculated from those three. Measuring it directly means ultracentrifugation, which is slow and expensive, so almost every LDL-C on almost every report in the world is an estimate.
The estimate works by subtracting VLDL cholesterol, which is not measured either, from non-HDL cholesterol. The whole problem is guessing how much VLDL-C there is. Friedewald solved this in 1972 by assuming triglycerides are always five times VLDL-C. That single fixed number is where the disagreement comes from: the real ratio varies from about 3 to 12 depending on how high the triglycerides are and how much non-HDL cholesterol is present.
Martin and colleagues at Johns Hopkins replaced the fixed 5 with an adjustable factor looked up from a 180-cell table, derived from 1.35 million lipid profiles. Sampson and colleagues at the NIH instead fitted a regression against the reference method that stays accurate up to triglycerides of 800 mg/dL, where Friedewald cannot be used at all.
At ordinary triglycerides the three land within a few mg/dL of each other and the choice hardly matters. At triglycerides above about 200 mg/dL, or when LDL-C is genuinely low, they separate — which is exactly the situation in which someone is deciding whether to start or intensify treatment. Above 400 mg/dL of triglycerides this calculator refuses to report a Friedewald result, because the equation is not valid there and a plausible-looking wrong number is worse than none.
The formula
non-HDL-C = TC − HDL-C
Friedewald LDL-C = TC − HDL-C − TG/5 (TG < 400 only)
Martin-Hopkins LDL-C = TC − HDL-C − TG/f
f = adjustable factor, 3.1–11.9, by TG and non-HDL-C
Sampson LDL-C = TC/0.948 − HDL-C/0.971
− (TG/8.56 + TG×non-HDL-C/2140 − TG²/16100)
− 9.44
All three are mg/dL equations — the coefficients only hold in those units, so mmol/L inputs are converted to mg/dL, solved, and converted back. Cholesterol converts at ×0.0259 and triglycerides at ×0.0113; using one factor for both is the commonest error on a lipid panel.
Worked example
Total cholesterol 220 mg/dL, HDL 45 mg/dL, triglycerides 250 mg/dL — a fairly typical raised-triglyceride panel:
- non-HDL-C = 220 − 45 = 175 mg/dL (4.53 mmol/L)
- Friedewald = 220 − 45 − 250/5 = 125 mg/dL (3.23 mmol/L)
- Martin-Hopkins factor for TG 250 and non-HDL-C 175 is f = 6.5
- Martin-Hopkins = 175 − 250/6.5 = 137 mg/dL (3.53 mmol/L)
- Sampson = 131 mg/dL (3.38 mmol/L)
- The three span 12 mg/dL on the same blood sample — enough to sit either side of the 130 mg/dL mark depending only on which equation the laboratory ran.
LDL cholesterol chart — the three equations compared
Calculated LDL-C in mg/dL (mmol/L beneath) for a panel with total cholesterol 200 and HDL 50 mg/dL, as triglycerides rise. Read down for your triglycerides.
| Triglycerides | Friedewald1972 | Martin-Hopkins2013 | Sampson2020 |
|---|---|---|---|
| 50 mg/dL0.56 mmol/L | 1403.62 mmol/L | 1363.53 mmol/L | 1413.64 mmol/L |
| 100 mg/dL1.13 mmol/L | 1303.36 mmol/L | 1293.34 mmol/L | 1323.41 mmol/L |
| 150 mg/dL1.69 mmol/L | 1203.10 mmol/L | 1243.20 mmol/L | 1233.19 mmol/L |
| 200 mg/dL2.26 mmol/L | 1102.84 mmol/L | 1183.05 mmol/L | 1152.98 mmol/L |
| 250 mg/dL2.82 mmol/L | 1002.59 mmol/L | 1142.96 mmol/L | 1072.77 mmol/L |
| 300 mg/dL3.39 mmol/L | 902.33 mmol/L | 1102.84 mmol/L | 1002.57 mmol/L |
| 350 mg/dL3.95 mmol/L | 802.07 mmol/L | 1032.67 mmol/L | 922.39 mmol/L |
| 450 mg/dL5.08 mmol/L | not validequation refuses | 992.56 mmol/L | 792.03 mmol/L |
| 600 mg/dL6.78 mmol/L | not validequation refuses | 822.12 mmol/L | 601.56 mmol/L |
| 800 mg/dL9.04 mmol/L | not validequation refuses | 591.53 mmol/L | 401.04 mmol/L |
Friedewald is blank at and above 400 mg/dL of triglycerides because the equation is not valid there, and Sampson above 800 mg/dL because that is the limit of its published validation. Notice the three agree closely at 50–150 mg/dL and separate sharply beyond 250. Every figure is computed by the same functions the calculator uses.
Martin-Hopkins adjustable factor — the full 180-cell table
The factor f that replaces Friedewald’s fixed 5. Find your triglyceride row and your non-HDL-C column; LDL-C is then non-HDL-C minus triglycerides divided by this number.
| Triglycerides, mg/dL | <100non-HDL-C | 100–129non-HDL-C | 130–159non-HDL-C | 160–189non-HDL-C | 190–219non-HDL-C | ≥220non-HDL-C |
|---|---|---|---|---|---|---|
| 7–49 | 3.5 | 3.4 | 3.3 | 3.3 | 3.2 | 3.1 |
| 50–56 | 4.0 | 3.9 | 3.7 | 3.6 | 3.6 | 3.4 |
| 57–61 | 4.3 | 4.1 | 4.0 | 3.9 | 3.8 | 3.6 |
| 62–66 | 4.5 | 4.3 | 4.1 | 4.0 | 3.9 | 3.9 |
| 67–71 | 4.7 | 4.4 | 4.3 | 4.2 | 4.1 | 3.9 |
| 72–75 | 4.8 | 4.6 | 4.4 | 4.2 | 4.2 | 4.1 |
| 76–79 | 4.9 | 4.6 | 4.5 | 4.3 | 4.3 | 4.2 |
| 80–83 | 5.0 | 4.8 | 4.6 | 4.4 | 4.3 | 4.2 |
| 84–87 | 5.1 | 4.8 | 4.6 | 4.5 | 4.4 | 4.3 |
| 88–92 | 5.2 | 4.9 | 4.7 | 4.6 | 4.4 | 4.3 |
| 93–96 | 5.3 | 5.0 | 4.8 | 4.7 | 4.5 | 4.4 |
| 97–100 | 5.4 | 5.1 | 4.8 | 4.7 | 4.5 | 4.3 |
| 101–105 | 5.5 | 5.2 | 5.0 | 4.7 | 4.6 | 4.5 |
| 106–110 | 5.6 | 5.3 | 5.0 | 4.8 | 4.6 | 4.5 |
| 111–115 | 5.7 | 5.4 | 5.1 | 4.9 | 4.7 | 4.5 |
| 116–120 | 5.8 | 5.5 | 5.2 | 5.0 | 4.8 | 4.6 |
| 121–126 | 6.0 | 5.5 | 5.3 | 5.0 | 4.8 | 4.6 |
| 127–132 | 6.1 | 5.7 | 5.3 | 5.1 | 4.9 | 4.7 |
| 133–138 | 6.2 | 5.8 | 5.4 | 5.2 | 5.0 | 4.7 |
| 139–146 | 6.3 | 5.9 | 5.6 | 5.3 | 5.0 | 4.8 |
| 147–154 | 6.5 | 6.0 | 5.7 | 5.4 | 5.1 | 4.8 |
| 155–163 | 6.7 | 6.2 | 5.8 | 5.4 | 5.2 | 4.9 |
| 164–173 | 6.8 | 6.3 | 5.9 | 5.5 | 5.3 | 5.0 |
| 174–185 | 7.0 | 6.5 | 6.0 | 5.7 | 5.4 | 5.1 |
| 186–201 | 7.3 | 6.7 | 6.2 | 5.8 | 5.5 | 5.2 |
| 202–220 | 7.6 | 6.9 | 6.4 | 6.0 | 5.6 | 5.3 |
| 221–247 | 8.0 | 7.2 | 6.6 | 6.2 | 5.9 | 5.4 |
| 248–292 | 8.5 | 7.6 | 7.0 | 6.5 | 6.1 | 5.6 |
| 293–399 | 9.5 | 8.3 | 7.5 | 7.0 | 6.5 | 5.9 |
| 400–13975 | 11.9 | 10.0 | 8.8 | 8.1 | 7.5 | 6.7 |
Reproduced from Martin SS, et al. JAMA. 2013;310(19):2061–2068, Figure 2. The factor falls as non-HDL-C rises and climbs as triglycerides rise — from 3.1 at the top right to 11.9 at the bottom left. Friedewald assumes 5.0 everywhere in this table.
LDL cholesterol conversion chart — mg/dL to mmol/L
Cholesterol and triglycerides do not convert with the same factor. Read across for the value on a US report and the equivalent on a UK, European or Australian one.
| Value on report | As cholesterolLDL, HDL, total | As triglyceridesTG only |
|---|---|---|
| 40 mg/dL | 1.03 mmol/L | 0.45 mmol/L |
| 55 mg/dL | 1.42 mmol/L | 0.62 mmol/L |
| 70 mg/dL | 1.81 mmol/L | 0.79 mmol/L |
| 100 mg/dL | 2.59 mmol/L | 1.13 mmol/L |
| 130 mg/dL | 3.36 mmol/L | 1.47 mmol/L |
| 150 mg/dL | 3.88 mmol/L | 1.69 mmol/L |
| 160 mg/dL | 4.14 mmol/L | 1.81 mmol/L |
| 190 mg/dL | 4.91 mmol/L | 2.15 mmol/L |
| 200 mg/dL | 5.17 mmol/L | 2.26 mmol/L |
| 300 mg/dL | 7.76 mmol/L | 3.39 mmol/L |
| 400 mg/dL | 10.35 mmol/L | 4.52 mmol/L |
| 500 mg/dL | 12.93 mmol/L | 5.65 mmol/L |
Cholesterol × 0.0259, triglycerides × 0.0113 — the conversion factors printed in Martin 2013. An LDL-C of 100 mg/dL is 2.59 mmol/L; triglycerides of 150 mg/dL are 1.69 mmol/L.
Frequently asked questions
- Why are there three different LDL cholesterol equations?
- Because LDL-C is never measured on a standard panel, only estimated, and the estimate depends on guessing how much VLDL cholesterol is present. Friedewald assumed in 1972 that triglycerides are always exactly 5 times VLDL-C. That ratio actually ranges from about 3.1 to 11.9 depending on triglyceride and non-HDL-C levels, so Martin-Hopkins (2013) looks the right factor up in a 180-cell table and Sampson (2020) fits a regression instead. All three are still in use by different laboratories today.
- When does the Friedewald equation stop working?
- Above 400 mg/dL of triglycerides (4.5 mmol/L) it should not be used at all — that limit is built into the equation's original validation and this calculator refuses to return a Friedewald number there. It also becomes unreliable well before that point: at triglycerides of 200–399 mg/dL, Martin and colleagues found Friedewald correctly classified an LDL-C below 70 mg/dL only 40.3% of the time, against 84.0% for their method.
- Which LDL equation is the most accurate?
- Against beta-quantification, the reference method, Sampson 2020 reported a root mean square error of 15.2 mg/dL for its own equation, 25.7 mg/dL for Martin-Hopkins and 32 mg/dL for Friedewald, with the gap widest in hypertriglyceridemia. Martin-Hopkins, however, was derived on 1.35 million profiles and independent validations often favour it below 400 mg/dL. The honest answer is that both newer equations beat Friedewald, and which of the two wins depends on the population.
- Is a direct LDL measurement better than a calculated one?
- A true direct measurement by beta-quantification with an ultracentrifuge is the reference standard, but it is slow, costly and rarely offered outside research. The "direct LDL" assays most laboratories sell are homogeneous enzymatic tests, which are not the reference method and have accuracy problems of their own at high triglycerides. For most people a modern calculated LDL-C from a good panel is entirely adequate; the case for direct measurement is strongest when triglycerides are very high or LDL-C is very low.
- How do I convert LDL cholesterol from mg/dL to mmol/L?
- Multiply mg/dL by 0.0259 for cholesterol — so an LDL-C of 100 mg/dL is 2.59 mmol/L, and 130 mg/dL is 3.36 mmol/L. Triglycerides use a different factor, 0.0113, because the molecule is much heavier: 150 mg/dL of triglycerides is 1.69 mmol/L. Applying the cholesterol factor to triglycerides is the single commonest unit error on a lipid panel. The calculator above accepts either unit.
- Why is my LDL different from the number on my lab report?
- Almost always because your laboratory used a different equation than the one you are reading. On a panel of total cholesterol 220, HDL 45 and triglycerides 250 mg/dL, Friedewald gives 125 mg/dL, Sampson 131 and Martin-Hopkins 137 — a spread of 12 mg/dL from one blood sample. Many labs have switched to Martin-Hopkins in recent years, so a number that changed without your diet changing may reflect the lab, not you.
- What counts as a normal or optimal LDL cholesterol?
- There is no single normal value, and "optimal" is not a figure this page will assert. What is sourceable is the US guideline classification Martin 2013 works in — bands at 70, 100, 130, 160 and 190 mg/dL (1.8, 2.6, 3.4, 4.1 and 4.9 mmol/L) — and the European list, which is not the same and cuts at 155 rather than 130 and 160. Those are classification boundaries, not targets: Sampson 2020 names 70, 100 and 190 mg/dL as treatment thresholds, and which one applies to you depends on your overall cardiovascular risk, not on a population range. Someone who has already had a heart attack is typically given a far lower target than someone with no risk factors. That is a conversation for your clinician, not a chart.
Sources
- [1]Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18(6):499–502
- [2]Martin SS, Blaha MJ, Elshazly MB, et al. Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile. JAMA. 2013;310(19):2061–2068
- [3]Sampson M, Ling C, Sun Q, et al. A New Equation for Calculation of Low-Density Lipoprotein Cholesterol in Patients With Normolipidemia and/or Hypertriglyceridemia. JAMA Cardiol. 2020;5(5):540–548
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Educational reference, not medical advice. Calculated LDL cholesterol is an estimate derived from three other measurements, not a diagnosis, and the three equations legitimately disagree. Interpretation, and any decision about treatment, belongs to your clinician.