What Are Milligrams?

Milligrams are very small measurements of solid weight in the international metric system. Specifically, a milligram is one-thousandth of a gram; to put it in concrete terms, the common mosquito weighs around 2 milligrams. In imperial (US) measurements, there are more than 28,000 milligrams in a single ounce. Metric units of measurement are widely used for scientific and medical purposes, even in the United States, which has not adopted the metric system for everyday use. Milligrams are commonly used to calculate dosages for medications, as even a small change in the amount of a drug can alter its effectiveness.

The metric system originated in 18th-century Europe, at a time when standards of measurement varied by nation and sometimes by region. Increasing international commerce and advances in science made a standard system of measurement essential. In the aftermath of the French Revolution of 1792, France’s new government proposed and accepted the earliest form of the metric system. In their eagerness to supplant old traditions, the French revolutionaries also proposed other new standards, such as a completely new calendar, but these were not as successful. Ironically, U.S. patriot and scientist Thomas Jefferson had proposed a similar system of measurements, but it was rejected by the U.S. Congress.

The metric system operates on basic units such as the gram, the meter, and the liter. Greater or lesser quantities are calculated by a factor of ten; a centimeter, for example, is one-tenth of a decimeter, which in turn is one-tenth of a meter. The metric system eventually evolved into the current system, called the International System of Units (SI), in official use by most nations around the world. A famous exception is the United States, which still uses the old British system, now known as the imperial or US system. Even in the United States, metric measurements are commonly used, appearing, for example, alongside imperial measurements on food packaging.

The gram is such a tiny amount of weight that the SI has adopted the kilogram as a more useful standard unit. A kilogram equals roughly 2.2 pounds in the imperial system. The milligram, being one-millionth of that weight, is clearly too small to be useful in casual day-to-day life. In scientific fields, however, such as chemistry, physics, and medicine, the milligram is a common unit of measurement. Only solid objects are weighed in grams or milligrams; liquid volume is calculated using the liter and the milliliter.

The most frequent use of milligrams in everyday life is to determine medication dosages. Both prescription and over-the counter medications are measured in milligrams, usually listed by the standard abbreviation "mg.” The effect of these chemicals on the body is so profound that determining very small amounts is crucial to managing the effectiveness of pharmaceutical products. With some very powerful medications, for example, the difference between an effective dose and an overdose can be a matter of milligrams.