Laboratory results for total cholesterol are reported in mg/dL in some countries and mmol/L in others, and the conversion runs through the molar mass: mmol/L = mg/dL × 10 ÷ 386.664, which for cholesterol is a factor of 0.0258622. A reference interval of 125–200 mg/dL is therefore 3.233–5.172 mmol/L, the same interval in different clothes.
The figure comes from the formula. Cholesterol is 27 × 12.011 (C) + 46 × 1.008 (H) + 15.999 (O), which is 386.664 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 27 of the 74 atoms in a formula unit are carbon, and they account for 324.297 g of the 386.664 g, or 83.87% by mass. The derivation table below breaks the whole molecule down element by element.
The factor is specific to the substance being measured, which is why a single "divide by 18" cannot be applied across a report: that figure belongs to glucose alone. For cholesterol the divisor is 38.6664, and using the wrong one produces a number that looks plausible and is wrong by a factor of two or three — the commonest error in reading a foreign result.
A membrane sterol and the reason lipid panels exist. Reported in mg/dL in the US and mmol/L elsewhere, with 200 mg/dL the familiar threshold. At 386.664 g/mol it is the heaviest of the 21 organic compounds covered here, and that ranking matters more than it looks: sucrose has a molar mass of 342.297 g/mol, so a gram of it contains 13% more formula units than a gram of cholesterol. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 7.7333 g of a nominal 386.664 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
mg/dL- The reported result in milligrams per decilitre
386.664- The molar mass of cholesterol in g/mol, derived from its formula
mmol/L- The same result in millimoles per litre
How it works, step by step
- Enter the result as reported, in mg/dL.
- It is multiplied by 10 to give mg/L.
- That is divided by 386.664 g/mol to give mmol/L.
- The reference interval is shown in both units so the converted figure can be read against it.
Worked examples
125 mg/dL of total cholesterol in mmol/L
125 × 0.0258622 = 3.2328 mmol/L, which is 3232.8 µmol/L. That result is at the bottom of the quoted interval of 125–200 mg/dL, or 3.233–5.172 mmol/L in the other unit.
162.5 mg/dL of total cholesterol in mmol/L
162.5 × 0.0258622 = 4.2026 mmol/L, which is 4202.6 µmol/L. That result is in the middle of the quoted interval of 125–200 mg/dL, or 3.233–5.172 mmol/L in the other unit.
280 mg/dL of total cholesterol in mmol/L
280 × 0.0258622 = 7.2414 mmol/L, which is 7241.4 µmol/L. That result is above the quoted interval of 125–200 mg/dL, or 3.233–5.172 mmol/L in the other unit.
How to read your score
Frequently asked questions
What is the molar mass of cholesterol (C27H46O)?
It is 386.664 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 27 × 12.011 (C) + 46 × 1.008 (H) + 15.999 (O). One mole of cholesterol therefore weighs 386.664 g, and a gram of it is 2.5862 mmol.
What percentage of cholesterol is carbon?
83.87% by mass. Each formula unit contains 27 carbon atoms contributing 324.297 g of the 386.664 g total, so 100 g of cholesterol contains 83.87 g of carbon and a kilogram contains 838.7 g of it.
How do I convert total cholesterol from mg/dL to mmol/L?
Multiply by 10 and divide by the molar mass, 386.664 g/mol — a single factor of 0.0258622 for cholesterol. To go back the other way, multiply the mmol/L figure by 38.6664.
What is the reference range for total cholesterol in both units?
Taking 125–200 mg/dL as the interval (desirable range), that is 3.233–5.172 mmol/L. Every laboratory publishes its own interval and the one printed on the report is the one that applies.
Why can I not use one conversion factor for the whole report?
Because the factor is the molar mass, and that differs for every analyte. For cholesterol it is 0.0258622; a factor borrowed from another test gives a result that looks reasonable and is wrong by whatever ratio separates the two molar masses.
What about mg/L and µmol/L?
A decilitre is 100 mL, so mg/dL × 10 is mg/L: 125 mg/dL is 1250 mg/L. Micromoles are millimoles × 1000, so the same result is 3232.8 µmol/L. Reports for trace analytes use µmol/L to avoid decimals.
Unit conversion table for cholesterol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 27 | 12.011 | 324.297 | 83.87% |
| Hydrogen (H) | 46 | 1.008 | 46.368 | 11.99% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 4.138% |
| Total — one mole of cholesterol | 386.664 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 386.664 g/mol.
| mg/dL | mmol/L | µmol/L | mg/L | Against reference |
|---|---|---|---|---|
| 62.5 mg/dL | 1.6164 | 1616.4 | 625 | below range |
| 82.308 mg/dL | 2.1287 | 2128.7 | 823.08 | below range |
| 102.12 mg/dL | 2.6409 | 2640.9 | 1021.2 | below range |
| 121.92 mg/dL | 3.1532 | 3153.2 | 1219.2 | below range |
| 141.73 mg/dL | 3.6655 | 3665.5 | 1417.3 | within range |
| 161.54 mg/dL | 4.1777 | 4177.7 | 1615.4 | within range |
| 181.35 mg/dL | 4.69 | 4690 | 1813.5 | within range |
| 201.15 mg/dL | 5.2023 | 5202.3 | 2011.5 | above range |
| 220.96 mg/dL | 5.7146 | 5714.6 | 2209.6 | above range |
| 240.77 mg/dL | 6.2268 | 6226.8 | 2407.7 | above range |
| 260.58 mg/dL | 6.7391 | 6739.1 | 2605.8 | above range |
| 280.38 mg/dL | 7.2514 | 7251.4 | 2803.8 | above range |
| 300.19 mg/dL | 7.7636 | 7763.6 | 3001.9 | above range |
| 320 mg/dL | 8.2759 | 8275.9 | 3200 | above range |
Conversion factor mg/dL × 10 ÷ 386.664 = mmol/L. Reference interval taken as 125–200 mg/dL (desirable range); laboratories publish their own intervals and those are the ones that apply to a result.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Uric acid | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose | C6H12O6 | 180.156 | 5.5507 |
| Aspirin | C9H8O4 | 180.159 | 5.5507 |
| Caffeine | C8H10N4O2 | 194.194 | 5.1495 |
| EDTA | C10H16N2O8 | 292.244 | 3.4218 |
| Sucrose | C12H22O11 | 342.297 | 2.9214 |
| Cholesterol (this page) | C27H46O | 386.664 | 2.5862 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.