The International System of Units (SI) sets standards for symbols, numbers, powers of 10 and their prefixes:

 

Symbol

 

  • Number
  •  
  • Numeral
  •  
  • Power of 10
  •  
  • Prefix

 

T

 

  • one trillion
  •  
  • 1,000,000,000,000
  •  
  • 10 12
  •  
  • tera-

 

G

 

  • one billion
  •  
  • 1,000,000,000
  •  
  • 10 9
  •  
  • giga-

 

M

 

  • one million
  •  
  • 1,000,000
  •  
  • 10 6
  •  
  • mega-

 

k

 

  • one thousand
  •  
  • 1,000
  •  
  • 10 3
  •  
  • kilo-

 

h

 

  • one hundred
  •  
  • 100
  •  
  • 10 2
  •  
  • hecto-

 

da

 

  • ten
  •  
  • 10
  •  
  • 10 1
  •  
  • deka-

 

(There is no symbol for whole number digits. You might write, "The shelter has 11 cats, 27 dogs, and one snake.")

 

  • one
  •  
  • 1
  •  
  • 10 0
  •  
  • no prefix

 

d

 

  • one-tenth
  •  
  • 0.1
  •  
  • 10 -1
  •  
  • deci-

 

c

 

  • one-hundredth
  •  
  • 0.01
  •  
  • 10 -2
  •  
  • centi-

 

m

 

  • one-thousandth
  •  
  • 0.001
  •  
  • 10 -3
  •  
  • milli-

 

µm

 

  • one-millionth
  •  
  • 0.000,001
  •  
  • 10 -6
  •  
  • micro-

 

n

 

  • one-billionth
  •  
  • 0.000,000,001
  •  
  • 10 -9
  •  
  • nano-

 

p

 

  • one-trillionth
  •  
  • 0.000,000,000,001
  •  
  • 10 -12
  •  
  • pico-

 

Examples:

 

  • gigabyte, megabyte, kilometer, hectopascal (air pressure), decimeter, centimeter, millimeter, micrometer, nanometer, picometer, etc.
  •  
  • In biology, we have decapod (deka) crustaceans (crabs) and millipedes and centipedes...
  •  
  • In geology we have calcareous nannoplankton (really small microfossils), etc.

 

The meter is really important. 1 meter (1m) =

 

  • 1000 millimeters (mm)
  •  
  • 100 centimeters (cm)
  •  
  • 10 decimeters (dm)
  •  
  • 0.001 kilometer (km)

 

And, there are many other common uses of the prefixes:

 

  • 1 micrometer (1µm) = 1 micron (1µ) (but micron was replaced by micrometer).
  •  
  • 1 kilogram (1 kg) = 1000 grams (1000 g).
  •  
  • 1 gram (1 g) = 0.001 kilogram (0.001 kg).
  •  
  • 1 liter (1 l) = 1000 milliliters (1000 ml).
  •  
  • 1 milliliter (1 ml) = 0.001 liter (0.001 l).