How Long is a Century? (Years, Months, Days & Seconds Explained)

How Long is a Century?

A century equals 100 years — or roughly 36,525 days, 1,200 months, 5,214 weeks, 876,600 hours, and about 3.15 billion seconds.
In the Gregorian calendar, a century begins with a year ending in 01 and ends with a year ending in 00 (for example, 2001–2100).

Quick Breakdown of a Century

Time Unit	Equivalent in 1 Century	Notes
Years	100	Base definition
Months	1,200	12 months × 100 years
Weeks	≈ 5,214	Rounded average
Days	≈ 36,525	Includes leap years
Hours	876,600	24 × days
Minutes	52,596,000	60 × hours
Seconds	3,155,760,000	60 × minutes

Did you know? Because of leap years, a century may contain 36,524 to 36,526 days, depending on how many leap days fall within that period.

What Exactly is a Century?

The word century comes from the Latin centum, meaning “hundred.”
It’s used to measure long periods of time — 100 consecutive calendar years.
For example, the 21st century CE runs from January 1, 2001 to December 31, 2100.

Why the 21st Century Starts in 2001 (Not 2000)

There was no year 0 in the Gregorian or Julian calendars.
After 1 BCE came 1 CE — so the first century covered 1–100, the second 101–200, and so on.
Following that pattern, the 21st century began on January 1, 2001, not 2000.

How Leap Years Affect a Century

A leap year occurs every 4 years — except for years divisible by 100 unless they’re also divisible by 400.
That rule keeps the calendar synchronized with Earth’s orbit (≈ 365.2422 days).

Example:

• 1900 was not a leap year.
• 2000 was a leap year.

Therefore, most centuries include about 24–25 leap years.

Historical Century Examples

Century	Years Covered	Highlights
18th Century	1701 – 1800	American & French Revolutions
19th Century	1801 – 1900	Industrial Age, Abolition of Slavery
20th Century	1901 – 2000	World Wars, Space Race, Digital Revolution
21st Century	2001 – 2100	AI Era, Sustainability & Global Connectivity

Other Calendars and Centuries

Different cultures track centuries differently:

• Julian calendar: Used before 1582; slightly less accurate, gaining ~3 days every 400 years.
• Islamic calendar: Lunar-based; its century equals about 97 solar years.
• Hebrew calendar: Adds leap months to stay aligned with seasons.

Frequently Asked Questions

Key Takeaways

• 1 century = 100 years = 36,525 days ≈ 3.15 billion seconds.
• We’re living in the 21st century (2001–2100).
• Leap years slightly adjust total days per century.
• Centuries provide structure for recording history and timekeeping.

See Also:

How Many Years Are in a Decade?