A medical assistant must understand how to convert between different units and systems of measurement because not all patients, medication directions, and prescriber orders operate with the same units in mind. The metric system is the preferred universal system of medical science, however it is not always what the general public uses.
In the United States, we make use of the imperial system that uses pounds, yards, inches, ounces, feet, etc. However, many other countries (and thus, many other patients) use the metric system. If, for example, the patient reports their daily water intake in ounces (oz), the medical assistant cannot simply plead that they cannot record the patient's intake because they do not know how to convert this to milliliters (mL)! They must commit that there are 30 mL in 1 oz to memory! or they can consult various resources including the internet. If the patient reports their weight in pounds (lbs), the medical assistant must be able to recall that there are 2.2 lbs per 1 kilogram (kg) and be able to do the math! This example particularly plays into the next section.
Medications also may not come in the medical assistant's preferred system of measurement and they may require such conversions. Some drugs can sometimes be prescribed with the units mL/mg/kg, read as milliliters per milligram per kilogram, meaning the amount of medication given is determined by the patient's weight in kilograms. If the conversion from one system to the other is unknown, the medication cannot be administered. Also some patients may not understand, have, or may have lost the tools needed to measure their medication. If it calls for 15 mL but they lost the cup, the medical assistant's knowledge of conversions from metric to the household system will allow them to communicate to the patient that they can also take 1 tablespoon (Tbs) or 3 teaspoons (tsp) and obtain the same amount.
Related to ability to communicate, prescribing doctors may order an amount of medication that does not align completely with the label. However, this cannot deter the medical assistant or other personnel from being able to do their job. They must be able to do the conversion.