Century

A century is a period of time consisting of one hundred years. The term derives from the practice of grouping years for chronological divisions into comparable units. It is called 'century' in English, 'siècle' in French, and 'قرن' in Arabic.

Centuries are typically numbered according to the Gregorian calendar. Years 1 to 100 constitute the 1st century, years 101 to 200 the 2nd century, and so on. Consequently, years 1901 to 2000 are the 20th century, while years 2001 to 2100 are the 21st century.

Counting systems

Two methods are in use. The standard method, based on arithmetic, ends a century in the year marking a hundred; for example, the 20th century ended on 31 December 2000. The alternative method, common in everyday usage, groups years sharing the same hundred digit, as in 'the 1900s', so that 2000 marks the start of a new period. This discrepancy has generated debate over when the 21st century began.

Relation to other time units

A century is longer than a decade (10 years) but shorter than a millennium (1,000 years). A millennium therefore contains ten centuries, and a century contains ten decades.

Use in history

Historians use centuries as a tool for dividing time; for example, when discussing social or political changes spanning long periods. However, century boundaries are calendar conventions and do not necessarily align with actual historical shifts; consequently, other terms such as 'the long nineteenth century' exist to mark periods that do not fit neatly into hundred-year units.