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Cell Biology
The World of Cells
The Size of Things
The Size of Things

In almost all branches of science today, the size of things is measured using the metric system. During the French Revolution, the government standardized all units of measurement into multiples of 10, which made it a lot easier to convert dimensions up and down the scale.

Slowly, this system has replaced the older, natural divisions of distance, temperature, volume, etc. Officially, it is called International System of Units, but is usually called the metric system.

International System of Units (The Metric System)
Dimension Common Unit Symbol American Equivalent
Length Meter m 39 inches
Mass Gram g 0.033 ounces
Volume Liter L 1.06 quarts
Dividing by Ten (Making smaller units)
1 meter = 1 gram = 1 liter =
102 centimeters (cm)
103 millimeters (mm)
106 micrometers (µm)
109 nanometers (nm)
1010 Angstroms (A)
103 milligrams (mg)
106 micrograms (µg)
109 nanograms (ng)
1012 picograms (pg)
103 milliliters (ml)
106 microliters (µl)
Using Symbols
Multiply basic
unit by
to get (Prefix) represented by
this symbol
10-1 or (0.1)
10-2 or (0.01)
10-3 or (0.001)
10-6 or (0.000001)
10-9 or (0.000000001)
10-12 or (0.000000000001)

Range of Sizes Armed with the table above, and all the prefixes and symbols, it is possible to measure almost anything that has physical dimensions.

For example:

One meter (m) is slightly longer than the American yard, and a centimeter (cm) is slightly less than half and inch. These are using of measure humans would use in their everyday lives, measuring distances to work, or dimensions of a book or table.

A millimeter (mm) is about is about the thickness of a pencil line, and is useful in science and engineering to ensure a close fit between parts, or make certain small dimensions more accurate.

A micrometer (µm) is at the limit of human vision and is about the thickness of a very thin piece of paper. These units would not be used in everyday human life, but in an engineering or scientific laboratory.

Below the micrometer, things get very small. A nanometer (nm) is only used in scientific laboratories and in this range of size a large, globular protein would be about 3 to 6 nm across.

© 2001, Professor John Blamire