What Is Decade?
A decade is a unit of time that means ten years. People use decades to talk about long periods in life, history, music, fashion and big changes in society. Instead of saying ten separate years, we group them together and call that group a decade.
Definition
A decade is a period of exactly ten years in a row.
You can think of it like this.
- 1 decade equals 10 years
- 2 decades equal 20 years
- 3 decades equal 30 years
We often use decades in these ways.
- To describe history, for example, the 1990s or the 1960s
- To describe a person age, for example, someone in their third decade of life
- To talk about trends, for example, fashion of the 80s
- To measure long plans, for example, a project that lasts several decades
History / Origin
The word decade has roots in very old languages that used words for the number ten.
- From Greek, the word dekas meant a group of ten
- From Latin, the word decas also meant a set of ten
Over time, this idea of a group of ten became linked to years. People needed an easy way to talk about long periods of time without listing each year. So the word decade became a simple name for ten years together.
By the time English was widely used, decade was already a common word for a ten year period. Today, it is an everyday word in history books, news reports, school lessons and normal conversation.
Symbol & Abbreviation
Unlike seconds, minutes or hours, the decade does not have a strict official symbol in science or in the International System of Units.
However, people sometimes use short forms in writing.
- dec or dec. for decade in informal notes
- 10 yr or 10 yrs to show ten years
- 10 y is sometimes used in charts or finance to mean ten years
These short forms are not formal rules. The safest and clearest way is to write the full word decade or the number of years, for example, ten years.
Current Use Around the World
The idea of a decade is used all over the world, even in countries with different calendars, because everyone needs a way to talk about ten year periods.
Here are some common uses.
- In history Teachers and books talk about events by decade, such as the 1940s or the 2000s.
- In culture People talk about music, clothes and movies from a certain decade, such as 80s pop music or 90s fashion.
- In personal life People may say things like, I worked there for two decades or we have been friends for three decades.
- In science Climate scientists look at decade long changes in temperature, rain and sea level.
- In business and government Long plans, big projects and population studies often cover one or more decades.
In English, decades of years are often written like this.
- 1920s means the years 1920 to 1929
- 1960s means the years 1960 to 1969
- 2020s means the years 2020 to 2029
Example Conversions
Here are some simple ways to convert between decades and other time units. To keep things easy, we will treat 1 year as 365 days. Real calendars include leap years, so exact day counts can be slightly different.
From decades to years
- 1 decade equals 10 years
- 2 decades equal 20 years
- 3 decades equal 30 years
- 5 decades equal 50 years
- 10 decades equal 100 years, which is 1 century
From years to decades
- 10 years is 1 decade
- 15 years is 1.5 decades
- 25 years is 2.5 decades
- 30 years is 3 decades
- 75 years is 7.5 decades
From decades to months
If we use 1 year as 12 months.
- 1 decade equals 10 years which is 120 months
- 2 decades equal 20 years which is 240 months
- 3 decades equal 30 years which is 360 months
From decades to days
If we use 1 year as 365 days, then.
- 1 decade equals 10 years which is about 3,650 days
- 2 decades equal 20 years which is about 7,300 days
- 3 decades equal 30 years which is about 10,950 days
From decades to centuries
- 1 century equals 10 decades
- 0.1 century equals 1 decade
- 0.5 century equals 5 decades
Related Units
A decade is one way to group years. Here are some related units of time that also use groups of years.
- Year The basic unit of time for our calendar, about 365 days.
- Half decade A period of 5 years.
- Lustrum A less common word from Latin that also means 5 years.
- Score An old word that means 20 years, used in some historic English texts.
- Century A period of 100 years, equal to 10 decades.
- Millennium A period of 1,000 years, equal to 10 centuries or 100 decades.
These units help people talk about both short and very long time periods in a clear way.
FAQs
How many years are in a decade?
There are exactly ten years in one decade. This is always true, no matter which years you choose.
Does a decade always start in a year ending with 0?
In everyday life, people usually think of decades as starting with a year that ends in 0 and ending with a year that ends in 9. For example, the 1990s are 1990 to 1999. Some historians use a different method and count from year 1 to year 10, but this is less common in daily use.
What are the 80s or 90s?
When people say the 80s they usually mean the decade from 1980 to 1989. The 90s usually means 1990 to 1999. These short names are often used to talk about music, fashion or events from that time.
Can a decade start at any year?
Yes. A decade is any period of ten years in a row. For example, from 2003 to 2012 is one decade, even though we do not call it the 2000s or the 2010s. So there are many overlapping decades, not just the calendar ones we name.
How do I say more than one decade?
The plural of decade is decades. For example, you can say two decades, several decades or many decades.
What is the difference between a decade and a century?
A decade is 10 years. A century is 100 years. This means that 1 century equals 10 decades.
Is decade an official scientific unit?
No. The decade is not a main unit in the International System of Units. However, it is widely used in science, for example in climate studies and geology, as a handy word for ten year periods.
Why do people use decades to talk about history?
Ten years is long enough for big changes in technology, culture and politics to happen. At the same time, it is short enough that people can still remember parts of it clearly. This makes the decade a useful size for studying and describing history.
How many decades are in a lifetime?
This depends on how long a person lives. If someone lives 70 years, that is 7 decades. If they live 80 years, that is 8 decades. If they live 90 years, that is 9 decades.
Is the term decade used the same way in all countries?
The exact word may sound different in other languages, but almost all cultures understand and use the idea of a ten year period. In English, the word decade is widely understood around the world.