How Many Years in a Millennium, Century, Decade?

Want to know how long is a century? what is a decade? Read on.

How Many Years in a Millennium Century Decade

Confused of how many years count in a Millennium, Century, Decade? Well, you won’t be anymore.

In this article, we will guide you through a detailed representation regarding the same. 

How Many Years in a Millennium?

Millennium is a period of 1,000 years.

  • 1 Millennium = 1000 Years

Millennia/Millenniums is a plural form of Millennium.

It is calculated according to the Gregorian calendar, which was put forth in 1582 and was eventually adopted by most countries.

According to Gregorian Calendar, a year is divided into 365-days and 12 months.

  • January, March, May, July, August, October, and December has 31 days each.
  • April, June, September, and November have 30 days.
  • February has 28 days in common years and 29 in leap years.

The calendar didn’t include a year 0 in the transition from BC to AD, and therefore the 1st millennium includes years 1–1000 and the 2nd the years 1001–2000. It was on January 1, 2001, when the 3rd millennium AD began.

You can calculate millennium to years using the formula:

  • Years = Millennium x 1000

How Many Years in a Century?

A century refers to the 100 consecutive calendar years.

  • 1 Century = 100 Years

The first century is defined as spanning years 1–100 and the twentieth century 1901-2000.

The twenty-first century started on January 1, 2001, and will end on 31 December 2100.

The number of the century is always equal to the number of hundreds increased by 1, excluding the years ending with 00.

How Many Years are in a Decade?

A decade is a period of ten years.

  • 1 Decade = 10 Years

For example, the period between 1921-1930, 1931-1940, and so on is considered to be a decade.

How Many Years in a Millennium Century Decade

Millennium, Century, Decade Comparison in Years

  • 1 Millennium = 10 Centuries = 1000 Years
  • 1 Century = 10 Decades = 100 Years
  • 1 Decade = 10 Years

1st Millennium · AD 1–1000

  • 1st Century – 10th Century
  • 0s – 990s

2nd Millennium · AD 1001–2000

  • 11th Century – 20th Century
  • 1000s – 1990s

3rd Millennium · AD 2001–3000

  • 21st Century
  • 2000s – 2090s

How Many Years in a Light year?

A light-year is defined as the distance light travels in one Earth year.

One light year is equal to the distance that light travels in one year, which is about ten trillion kilometers or six trillion miles.

Mathematically, one light-year is equal to approx 6.5×10^5 earth years.

Light travels at a speed of 186,282 miles per second, and if you were a space shuttle that traveled five miles per second, it would take you about 37,200 human years to travel one light year.

How Many Years in a Generation?

A generation refers to the group of people born and living at about the same time. 

It is also generally described as the period during which children are born, become adults, and begin to have children.

A generation period is usually considered to be about 20–⁠30 years.

The breakdown of generation by year looks like this:

  • Baby Boomers: Born between 1946 and 1964
  • Gen X:  Born between 1965 and 1979/80
  • Gen Y:  Born between 1981 and 1994/6
  • Gen Z:  Born between 1997 and 2012
  • Gen A: Born between 2013 and 2025


How long is a decade, century, and millennium?

A decade consists of ten years, a century- hundred, and millennium thousand.

How many decades are in a century?

There are ten decades in a century.

What is after a millennial?

After millennia comes terasecond.

What century are we now?

We’re currently in the 21st century.

What is a period of 12 years called?

A period of 12 years is called Duodecennial.

What is another word for 10 years?

Another word for 10 years is decennial.


I hope that you can now keep an estimated count on Millennium, Century, Decade with ease. 

Feel free to suggest such interesting topics, we would love to cover them on our blog. 

I am a thorough nerd who completely indulges into books when handed one, unless it is a hard-boiled fiction. Apart from reading and surfing shows on Netflix, I love to vent my emotions out through writings.