Centillion is a big number. It (centillion) refers to different quantities based on locality of usage.

North American system

• In Canadian
  Canada
  Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
  
   and U.S.
  United States
  The United States of America is a federal constitutional republic comprising fifty states and a federal district...
  
   usage, two centillion is 10³⁰³+10³⁰³.
• While Britain
  United Kingdom
  The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
  
  , Australia
  Australia
  Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
  
   and New Zealand
  New Zealand
  New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
  
   traditionally employed the European usage, recently they have largely switched to the U.S. version.

10³⁰³ is a thousand times more than a novemnonagintillion.
10³⁰³ is a thousandth of an uncentillion.

10³⁰³ is a quinquagintilliard, or a thousand quinquagintillion, in the European system.

It is believed to be the largest number with a conventional name, and the second largest named number after googolplex, discounting such curiosities as millillion (10³⁰⁰³) which, though not officially accepted, are legitimately coined and widely used in some circles.

European system

• In traditional Europe
  Europe
  Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
  
  an usage, one centillion is 10⁶⁰⁰, i.e. (10⁶)¹⁰⁰, the number with a hundred times as many zeroes as a million).

10⁶⁰⁰ is a thousand times more than a novemnonagintilliard.
10⁶⁰⁰ is a thousandth of a centilliard.

10⁶⁰⁰ is a million times more than a novemnonagintillion.
10⁶⁰⁰ is a millionth of an uncentillion.

Related terms

• hundred
  100 (number)
  100 is the natural number following 99 and preceding 101.-In mathematics:One hundred is the square of 10...
  
  
• million
  Million
  One million or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001. The word is derived from the early Italian millione , from mille, "thousand", plus the augmentative suffix -one.In scientific notation, it is written as or just 106...
  
  
• billion (disambiguation)
• trillion (disambiguation)
• decillion
• centilliard
• names of large numbers
  Names of large numbers
  This article lists and discusses the usage and derivation of names of large numbers, together with their possible extensions.The following table lists those names of large numbers which are found in many English dictionaries and thus have a special claim to being "real words"...