Friedewald equation · mg/dL and mmol/L
Your LDL cholesterol, calculated and then explained.
Type the three numbers from a standard lipid panel. You get the LDL cholesterol the Friedewald equation produces, the rest of the panel worked out beside it, and the arithmetic printed in full — including the triglyceride level at which the equation stops being trustworthy.
- No ads, no accounts, no tracking scripts.
- Every step of the arithmetic shown.
- Guardrails at the exact limits where the equation fails.
- mg/dL and mmol/L, each calculated the way it is published.
Lipid panel
Your three numbers
Copy them straight off the report. Nothing is sent anywhere — the arithmetic runs in this page.
Units on your report
Every cholesterol-carrying particle added together.
The protective fraction. Reports often write it HDL-C.
The one the equation leans on hardest. Needs a fasting sample.
Add risk context (optional)
Sex
HDL cholesterol is the only measurement here with different cut-points by sex: below 40 mg/dL (1.03 mmol/L) is low in men, below 50 mg/dL (1.29 mmol/L) in women.
Cardiovascular risk
Adds the LDL-C treatment goal for that risk category. It never changes the calculation.
Your results
LDL cholesterol · Friedewald
—mg/dL
Fill in all three values to see a result.
Everything else in the panel
The same numbers, worked through and converted, so you can hand the page to anyone who reads the other unit.
| Measurement | mg/dL | mmol/L | Category |
|---|---|---|---|
| Non-HDL cholesterol | — | — | — |
| VLDL cholesterol | — | — | Estimated from triglycerides |
| Total cholesterol | — | — | — |
| HDL cholesterol | — | — | — |
| Triglycerides | — | — | — |
Ratios and indices
Reported for completeness. These have no single agreed cut-point, so no category is shown for them.
- Total cholesterol / HDL cholesterol
- —
- LDL cholesterol / HDL cholesterol
- —
- Triglycerides / HDL cholesterol (mg/dL)
- —
- Atherogenic index of plasmalog₁₀(TG / HDL-C), both in mmol/L
- ——
Treatment goal for that risk category
—
Targets are population-level guidance from the 2019 ESC/EAS dyslipidaemia guidelines; the 2018 AHA/ACC guideline sets statin intensity by risk group instead of a numeric LDL-C target. Your own target is a clinical decision — this page cannot make it.
Show your work
LDL-C = TC − HDL-C − TG / 5
The equation as published in 1972, with the divisor for the unit you chose.
Category cut-points: National Cholesterol Education Program (NCEP) Expert Panel; Grundy SM, Stone NJ, Bailey AL, et al. Full citations at the foot of this page.
Reference
What the number means
These categories are how the guidelines describe a population. They are not the goal for any one person — the goal is set by overall cardiovascular risk.
| Category | mg/dL | mmol/L | What it means |
|---|---|---|---|
| Optimal | Under 100 | Under 2.59 | Below the goal for every risk category in the guidelines. |
| Near optimal / above optimal | 100–129 | 2.59–3.35 | Above optimal, but still at or below the goal for low and moderate risk. |
| Borderline high | 130–159 | 3.36–4.13 | Above the goal for anyone at high risk; usually where treatment starts being discussed. |
| High | 160–189 | 4.14–4.90 | From 160 mg/dL (4.14 mmol/L) most guidelines recommend treatment for most people. |
| Very high | 190 and over | 4.91 and over | From 190 mg/dL (4.91 mmol/L), which on its own counts as high risk and raises the question of familial hypercholesterolaemia. |
Source: National Cholesterol Education Program (NCEP) Expert Panel and Grundy SM, Stone NJ, Bailey AL, et al. Both unit columns describe the same cut-points: 100 mg/dL is 2.59 mmol/L, 190 mg/dL is 4.91 mmol/L.
The arithmetic
How the Friedewald equation works
One subtraction and one division, both of which have to be done in the unit the equation was published for.
In 1972 Friedewald, Levy and Fredrickson needed an LDL cholesterol result that did not require an ultracentrifuge, because preparative ultracentrifugation was far too slow for routine laboratory use. Their answer was to stop measuring LDL altogether and to estimate it by difference.
Two of the three terms are measured directly: total cholesterol and HDL cholesterol. The third — the cholesterol sitting inside VLDL particles — is the one nobody measures, so the equation infers it from triglycerides. That inference is the whole equation, and also its whole weakness: it holds only while VLDL composition is normal and the sample was taken fasting.
mg/dL LDL-C = TC - HDL-C - TG / 5 mmol/L LDL-C = TC - HDL-C - TG / 2.2
Where the divisor comes from. In fasting plasma a VLDL particle carries roughly five times as much triglyceride as cholesterol by mass. Dividing triglycerides by 5 therefore turns a triglyceride concentration into an estimate of VLDL cholesterol, and subtracting it strips VLDL out of total cholesterol.
Why the SI form uses 2.2. Dividing by 5 in mg/dL is equivalent to dividing by about 2.18 in mmol/L, not 2.2. The SI literature and laboratory practice use 2.2, so this calculator does too: enter mmol/L and it divides by 2.2, enter mg/dL and it divides by 5. The consequence is that the same physical panel can land about 0.01 mmol/L apart between the two paths, which is why the page always states which unit it computed in.
Worked example
TC 200 mg/dL, HDL-C 50 mg/dL, TG 150 mg/dL
LDL-C = 200 - 50 - 150 / 5
= 200 - 50 - 30
= 120 mg/dLThe same panel in SI units — TC 5.17, HDL-C 1.29, TG 1.69 mmol/L — gives 5.17 − 1.29 − 1.69/2.2 = 3.11 mmol/L. Converting the 120 mg/dL answer across gives 3.10 mmol/L: the 0.01 mmol/L divergence described on the left.
The derivation, the original paper and the alternatives are onthe Friedewald equation page.
Limits
When not to trust the calculated number
The equation has a documented ceiling, and a calculator that hides it is more dangerous than no calculator at all.
Triglycerides at or above 400 mg/dL (4.5 mmol/L)
The hard limit, written into the original paper and repeated by every guideline since. At high triglycerides the relationship between triglyceride mass and VLDL cholesterol breaks down and the equation underestimates LDL cholesterol, sometimes substantially.
Use instead: non-HDL cholesterol, which needs no equation at all; a direct measured LDL; or a result calculated with the Martin–Hopkins or Sampson method. This calculator flags any panel at or above the limit and still shows the arithmetic, so you can see how far the estimate may be off.
Triglycerides below about 50 mg/dL (0.6 mmol/L)
At the other end the VLDL estimate becomes negligible and unstable, so the calculated LDL cholesterol can come out inflated. Laboratories see this in fasting samples from people on very low-fat diets and in some genetic lipid disorders.
A non-fasting sample
Triglycerides rise after a meal, often by well over 100 mg/dL. Because the equation reads every triglyceride molecule as VLDL, a postprandial sample makes the VLDL estimate too large and pushes the calculated LDL cholesterol down. The 5 assumes fasting plasma.
Abnormal lipoproteins, or very low LDL
Chylomicronaemia and type III dyslipidaemia put triglyceride into particles the divisor of 5 was never meant to describe. At low LDL cholesterol — the range people on statins live in — a fixed divisor also carries more relative error, which is precisely the problem the Martin–Hopkins method was built to fix.
What to use instead
Martin–Hopkins (adjustable 180-cell) method
Replaces the fixed factor of 5 with an adjustable factor drawn from a 180-cell table indexed by triglyceride and non-HDL cholesterol levels. It stays accurate at triglyceride levels where the Friedewald equation is no longer valid.
Useful when: Non-fasting samples and triglycerides between 400 and 800 mg/dL (4.5–9 mmol/L).
Sampson (NIH) equation
A regression equation published by the NIH that is less biased than Friedewald at low LDL cholesterol and high triglyceride levels, and which has been adopted by some large laboratories.
Useful when: Low LDL cholesterol and/or raised triglycerides.
Direct measurement (homogeneous assay)
The laboratory measures LDL cholesterol directly instead of estimating it. Also the only way to report LDL cholesterol when triglycerides are above 400 mg/dL.
Useful when: Triglycerides above 400 mg/dL, or when an exact value is needed for treatment decisions.
Targets
The goal depends on your risk, not on the number
LDL cholesterol goals come from cardiovascular risk categories rather than from one cut-point. These are the ESC/EAS figures; the AHA/ACC approach is noted underneath because it works differently.
| Risk category | LDL-C goal | Also required | Who this describes |
|---|---|---|---|
| Very high risk | Below 55 mg/dL(1.40 mmol/L) | plus at least a 50% reduction from baseline LDL-C | Established atherosclerotic cardiovascular disease, or diabetes with target-organ damage or several major risk factors, or severe chronic kidney disease. |
| High risk | Below 70 mg/dL(1.80 mmol/L) | plus at least a 50% reduction from baseline LDL-C | A markedly raised single risk factor — for example LDL-C of 190 mg/dL (4.9 mmol/L) or more — or diabetes of long duration, or moderate chronic kidney disease. |
| Moderate risk | Below 100 mg/dL(2.60 mmol/L) | — | Younger people with type 1 diabetes, or diabetes without additional risk factors and a short duration. |
| Low risk | Below 116 mg/dL(3.00 mmol/L) | — | No established cardiovascular disease, diabetes, or major modifiable risk factor. |
Targets are population-level guidance from the 2019 ESC/EAS dyslipidaemia guidelines; the 2018 AHA/ACC guideline sets statin intensity by risk group instead of a numeric LDL-C target. Your own target is a clinical decision — this page cannot make it.
The rest of the panel
Four measurements, four pages: the composite that stays valid when triglycerides are high, the conversion factors, the full category chart, and the equation itself.
- Non-HDL cholesterol calculatorTotal cholesterol minus HDL cholesterol — the part of the panel that carries the atherogenic particles, and the measurement that stays valid when triglycerides are high.
- mg/dL to mmol/L converterConvert total cholesterol, LDL-C, HDL-C and triglycerides between mg/dL and mmol/L, using the separate factors each analyte actually needs.
- LDL cholesterol chartEvery LDL-C category from optimal to very high, in mg/dL and mmol/L side by side, with the treatment goals that sit underneath them.
- The Friedewald equationThe 1972 formula, why the divisor is 5 in mg/dL and 2.2 in mmol/L, and the exact triglyceride level at which it stops being trustworthy.
Questions
LDL cholesterol questions, answered
The questions this calculator gets asked, answered in full sentences rather than one line each.
What is a normal LDL cholesterol level?
There is no single normal value, because the level that matters depends on your overall cardiovascular risk. For reference, the Adult Treatment Panel III classification calls below 100 mg/dL (2.59 mmol/L) optimal, 100–129 mg/dL near optimal, 130–159 mg/dL borderline high, 160–189 mg/dL high, and 190 mg/dL (4.9 mmol/L) or above very high. Treatment goals sit far below the top of those bands for people at higher risk: below 70 mg/dL (1.8 mmol/L) for high risk and below 55 mg/dL (1.4 mmol/L) for very high risk in the 2019 ESC/EAS guidelines.
How is LDL cholesterol calculated?
The standard calculation is the Friedewald equation, published in 1972: LDL-C = total cholesterol − HDL cholesterol − triglycerides ÷ 5 in mg/dL, or triglycerides ÷ 2.2 in mmol/L. The division estimates the cholesterol carried in VLDL particles, which are not measured directly. LDL itself is never measured, which is why the result is called a calculated or estimated LDL rather than a measured one.
Why does the equation divide triglycerides by 5?
In mg/dL the divisor of 5 comes from the composition of a VLDL particle. In the fasting state VLDL carries roughly one fifth as much cholesterol as triglyceride by mass, so dividing the triglyceride concentration by 5 estimates the cholesterol that VLDL is carrying, and subtracting it leaves the cholesterol in LDL. The SI form uses 2.2 rather than the mathematically equivalent 2.18, which is why a panel calculated in mmol/L can differ by about 0.01 mmol/L from the same panel calculated in mg/dL.
When is the Friedewald equation inaccurate?
It fails in four situations. Triglycerides of 400 mg/dL (4.5 mmol/L) or more: the assumption behind the divisor of 5 breaks down and the equation underestimates LDL cholesterol, which is why the original paper and every guideline since set that limit. Very low triglycerides, below about 50 mg/dL (0.6 mmol/L): the VLDL estimate becomes unreliable. Non-fasting samples: triglycerides rise after a meal, so the VLDL estimate is too large and LDL comes out too low. And conditions with abnormal lipoproteins, such as chylomicronaemia or type III dyslipidaemia, where a fixed divisor does not describe the particles present.
Do I need to fast for this calculation?
Yes. The divisor of 5 assumes fasting triglyceride levels, and a non-fasting sample can raise triglycerides enough to push the calculated LDL cholesterol down by a clinically meaningful amount. Most laboratories ask for 9 to 12 hours of fasting before a lipid panel, although some screening programmes now accept non-fasting samples and interpret triglycerides and non-HDL cholesterol rather than a calculated LDL.
Why is my calculated LDL different from the number on my lab report?
Three common reasons. Rounding: reports round the inputs before calculating, or round the result, so a value can move by a milligram or two. A different equation: some laboratories now use the Martin–Hopkins adjustable factor or the Sampson equation instead of Friedewald, and the three disagree most at high triglyceride or low LDL levels. A direct measurement: some assays measure LDL cholesterol physically rather than estimating it, which sidesteps the equation and is the right approach when triglycerides are above 400 mg/dL.
Four more questions, including what to do above 400 mg/dL triglycerides, are onthe full FAQ page.
References
- 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. PubMed (opens in a new tab)
- 2.National Cholesterol Education Program (NCEP) Expert Panel. Third Report of the NCEP Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), final report. Circulation. 2002;106(25):3143-3421. PubMed (opens in a new tab)
- 3.Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol. Circulation. 2019;139(25):e1082-e1143. PubMed (opens in a new tab)
- 4.Mach F, Baigent C, Catapano AL, et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk. Eur Heart J. 2020;41(1):111-188. PubMed (opens in a new tab)
- 5.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. PubMed (opens in a new tab)
- 6.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. PubMed (opens in a new tab)
- 7.Dobiášová M, Frohlich J. The plasma parameter log (TG/HDL-C) as an atherogenic index: correlation with lipoprotein particle size and esterification rate in apoB-lipoprotein-depleted plasma (FER(HDL)). Clin Biochem. 2001;34(7):583-588. PubMed (opens in a new tab)
Content last reviewed 16 September 2026.Every cut-point and formula on this page is taken from the sources above.
The number is the easy part. Knowing when to distrust it is the point.
Run your panel through the Friedewald equation, see every step, and get told plainly when the result should not be acted on.