Cholesterol is a waxy solid that's suspended in the blood plasma. It has several important uses in the body but excess cholesterol in the blood is associated with an increased risk of heart disease. The concentration of cholesterol in the blood is routinely measured as part of a blood test. You must ensure your cholesterol level is measured in the correct units, though, when you compare it to the desired reference range.

Obtain a cholesterol value in milligrams of cholesterol per deciliter of blood (mg/dl.) A milligram is a unit of mass equal to 1/1000 of a gram and a deciliter is a unit of volume equal to 1/10 of a liter.

Convert mg/dl into milligrams per liter (mg/l.) A liter is 10 times more volume than a deciliter, so multiply mg/dl by 10 to get mg/l.

Determine the ratio to convert milligrams of cholesterol to millimoles (mmol) of cholesterol. The ratio of milligrams to millimoles is equal to the ratio of grams to moles. You therefore need to know the mass in grams of a mole of cholesterol. This quantity is also known as the molecular weight of cholesterol.

You can find the molecular weight of cholesterol by taking the sum of the atomic masses of the atoms in a molecule of cholesterol (which has a molecular formula of C27H46O). The atomic weight of carbon is 12.0107, the atomic weight of hydrogen is 1.00794 and the atomic weight of oxygen is 15.9994. The molecular weight of cholesterol is therefore 12.0107*27 + 1.00794*46 + 15.9994 = 386.65354.

Divide the cholesterol level in mg/l by the molecular weight of cholesterol (386.65354) to get the cholesterol level in mmol/l. The conversion factor for converting cholesterol in mg/dl to cholesterol in mmol/l is therefore 10/386.65354, or approximately 0.0259.