What is a Century?

The century equals exactly 100 years and is the standard unit for major historical periods, generational shifts, and long-term cultural analysis. The word comes from the Latin 'centum' (one hundred). Centuries are conventionally numbered with the year 1 starting the 1st century, so the 21st century runs from 2001 to 2100 (a common confusion: the year 2000 was the last year of the 20th century, not the start of the 21st). Centuries are central in historical writing — 'the 18th century,' 'mid-19th-century literature' — and in cricket, where a 'century' is a batsman scoring 100 runs in a single innings. The century relates to the year (100 years = 1 century), the decade (10 decades = 1 century), and the millennium (10 centuries = 1 millennium). The Roman 'centurion' commanded a century of soldiers (originally 100 men).

Visual reference for how the century relates to other time units. Each row links to the full converter for that pair.

• Historical period and era references
• Long-term climate and geological trends
• Cricket batting milestones (a "century" = 100 runs)

• ✓1 century = 100 years = 36,525 days.
• ✓Ordinal numbering: 21st century = 2001–2100 (strict), 2000–2099 (popular).
• ✓Rarely useful in engineering — years or decades are more practical.

• ✗Writing 20th century when meaning 1900s — they overlap but differ in first/last year.
• ✗Treating century exactly as 100 × 365 days — ignores leap years.
• ✗Mixing calendar systems (Gregorian vs. Julian) across centuries — matters pre-1582.