*The Scale of Things - Nanometers and More. (Source: Office of Science, U.S. Department of Energy) (click on image to enlarge)*

A metric prefix precedes a basic unit of measure to indicate a decimal multiple or a fraction of that unit. The 20 metric prefixes are used for describing quantities of the *International System of Units* (SI) in a more concise manner.

There are 20 metric prefixes that are currently recognized for use, ranging from the smallest yocto (1 quadrillionth) to the largest yotta (1 quadrillion). They have been specified by the International Bureau of Weights and Measures (BIPM) for the SI.

These prefixes are applied to metric units of measurement: mass, volume, weight, length, time, temperature, angle and energy. Metric prefixes are also widely used outside the metric SI system such as gigabyte, megaparsec or megaelectronvolt.

SI prefixes for submultiples (smaller quantities or sub units) are formatted with all lowercase symbols while prefixes for multiples (larger quantities or whole units) use uppercase symbols with the exception of three: kilo (k), hecto (h) and deka (da). So a gigahertz is GHz and a femtosecond is fs.

Conversions between metric system units are easy because the system is based on powers of ten. For example, there are 100 centimeters in 1 meter, 1000 meters in 1 kilometer. Conversely, there are 1 billion nanometers in 1 meter. Metric prefixes are used to distinguish between units of different size. These prefixes all derive from either Latin or Greek terms.

The table below lists the most common metric prefixes and their relationship to the central unit that has no prefix. Length is used as an example to demonstrate the relative size of each prefixed unit.

Prefix

Symbol

Multiplier

Exponential

yotta

Y

1,000 000 000 000 000 000 000 000

1024

zetta

Z

1,000 000 000 000 000 000 000

1021

exa

E

1,000 000 000 000 000 000

1018

peta

P

1,000 000 000 000 000

1015

tera

T

1,000 000 000 000

1012

giga

G

1,000 000 000

109

mega

M

1,000 000

106

kilo

K

1,000

103

hecto

h

100

102

deca

da

10

101

1

100

deci

d

0.1

10-1

centi

c

0.01

10-2

milli

m

0.001

10-3

micro

µ

0.000 001

10-6

nano

n

0.000 000 001

10-9

pico

p

0.000 000 000 001

10-12

femto

f

0.000 000 000 000 001

10-15

atto

a

0.000 000 000 000 000 001

10-18

zepto

z

0.000 000 000 000 000 000 001

10-21

yocto

y

0.000 000 000 000 000 000 000 001

10-24

The estimated total annual amount of digital data created, consumed, and stored globally is about 64 zettabytes in 2020, expected to rise to 180 zettabytes by 2025.

A distance of one terameter is roughly one light hour. The diamter of Earth's orbit around the Sun is about 0.3 terameters

Terahertz radiation consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz).

The hard disk capacity of modern computers has reached the terabyte range.

The clock speeds of CPUs in modern computers has reach the gigahertz (GHz) range.

Megapixels are commonly used to express the number of image sensor elements of digital cameras or the number of display elements of digital displays.

Widely used for distance (kilometer) or weight (kilogram).

The head of a pin is about 2 millimeters in diameter. The smallest distances the human eye can resolve is around 0.02 to 0.04 mm. Red ants are about 5 mm long.

Also expressed by the Greek letter µ. Biology often deals with objects in the micrometer range such as bacteria (1-10 µm), red blood cells (7-8 µm), pollen (&sim 100 µm) or mites (&sim 500 µm).

A strand of human DNA is 2.5 nanometers in diameter. A single gold atom is about a third of a nanometer in diameter

The Bohr diameter of hydrogen atom in ground state is 106 picometers

The diameter of a proton is 1.6 femtometers. Molecules react within femtoseconds. The light pulses produced with the most modern lasers last just a few femtoseconds to attoseconds

Attosecond physics deals with ultrafast processes in nature. For instance, the motion of electrons in atoms lasts just a few attoseconds.

Take a look of examples across a range from centimeter to nanometer:

View the Milky Way at 10 million light years from the Earth. Then move through space towards the Earth in successive orders of magnitude until you reach a tall oak tree. After that, begin to move from the actual size of a leaf into a microscopic world that reveals leaf cell walls, the cell nucleus, chromatin, DNA and finally, into the subatomic universe of electrons and protons.

(Secret Worlds: The Universe Within. © Michael W. Davidson and The Florida State University)

Once the tutorial has completely downloaded, a set of the arrows will appear that allow the user to increase or decrease the view magnitude in Manual mode. Click on the Auto button to return to the Automatic mode.

Notice how each picture is actually an image of something that is 10 times bigger or smaller than the one preceding or following it. The number that appears on the lower right just below each image is the size of the object in the picture. On the lower left is the same number written in powers of ten, or exponential notation. Exponential notation is a convenient way for scientists to write very large or very small numbers.