Math in Science: Comparing Metric Units of Mass and Weight

In this tutorial, we’ll discuss grams as the basic unit used to measure mass, and, using everyday objects as examples, try to give you an idea of the size and scale of various measurements based on grams. Let’s quickly review the metric staircase. Remember that as you move up the staircase, mass measurements increase by factors of 10, and as you move down the staircase, mass measurements decrease by factors of 10. So let’s start with the basic metric unit of mass – the gram. You may notice that we use the word “mass” here instead of “weight.” In the sciences, a distinction is made between mass and weight. Weight is a measure of the pull of gravity on an object. So an object’s weight would be different if it were weighed on Earth vs. the moon because of the difference in gravitational pull. However, an object’s mass would remain the same in both places because mass measures the amount of substance in an object. But, as long as you’re planning on only measuring objects on Earth, you can pretty much use the terms mass and weight interchangeably. For instance, a paperclip (on Earth) typically weighs about one gram. It also has the mass of one gram. In the lab, scientists often deal with mass measurements that are smaller than grams. So let’s look at these smaller measurements next. Decigrams are 10 times smaller than grams. A decigram is equal to one tenth of a gram, or about the mass of a large drop of water. Centigrams are 100 times smaller than grams. A small ant weighs about a centigram. Milligrams are a thousand times smaller than grams. A particle of baking powder weighs about a milligram. Micrograms are a million times smaller than grams. They’re extremely small! A human ovum weighs about a microgram. Nanograms are even smaller than micrograms at one billionth of a gram. The average human cell weighs about one nanogram. Let’s return to grams for a moment as the basic unit of measurement. Scientists in the field often work with measurements that are larger than a gram, so let’s look at these larger units next. A decagram is ten times larger than a gram. This is about the mass of four pennies. A hectogram is 100 times larger than a gram. A bag of rice weighs about a hectogram. A kilogram is a thousand times larger than a gram. It is equal to about 2.2 pounds, or about the weight of a book or small laptop. A megagram is equal to one million grams. A megragram is also commonly referred to as a metric ton. This is roughly the weight of an elephant. A gigagram is equal to a billion grams. This is about the weight of 1000 elephants, or half the launch weight of the space shuttle. While it makes sense to understand all these units of measurement, the ones that are most commonly used in the sciences include: nanogram, microgram, milligram, gram, kilogram and megagram (or metric ton).

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