**One decade has ten years, and to get the number of decades in one year, you have to divide 1/10 = 0.1 decades. So there are 0.1 decades in one year. On the other hand, we multiply by ten when converting decades to years.**

It is possible to convert any number of years to decades by dividing by ten or any number of decades to years by multiplying them by 10.

This article highlights how to convert years to decades and vice versa, the definition of year and decade, main seasons in a year, usage of a decade, and methods of denominating decades. Read on!

**How can you convert different years to decades and vice versa?**

It is possible to convert any number of years to decades when you divide by 10. The following table shows different years and the equivalent number of decades.

Number of years | Equivalent number of decades |

One | 0.1 |

Two | 0.2 |

Three | 0.3 |

Four | 0.4 |

Five | 0.5 |

Ten | 1 |

Fifteen | 1.5 |

Twenty | 2 |

**What is the definition of a year?**

The word year has several definitions, including;

- A year is a period that the earth takes to revolve around the sun, and it is abbreviated as yr. or y. A standard year has 365 days, while a leap year has 366 days and occurs after every four years (as per the Gregorian calendar).
- It is a period of 12 months starting from 1
^{st}January to 31^{st}December - The time it takes a planet to revolve around the sun once
- The period when a school is in session (for example nine months) other than a calendar year.

**What are the main seasons in a year?**

A season is a length of time in a year distinguished by specific climatic conditions. One year has four seasons: Spring, Summer, Fall, and Winter, with each season having its unique temperature, light, and weather patterns every year.

The table below shows these seasons in the Northern Hemisphere.

Season | When it begins |

Winter | 21^{st} or 22^{nd} December – it has the shortest daylight period |

Summer | 20^{th} or 21^{st} June – longest daylight in the year |

Spring | Begins on the equinox – 20^{th} or 21^{st} March |

Fall/Autumn | It starts on the equinox – 22^{nd} or 23^{rd} September. |

**What is a decade?**

The word ‘decade’ comes from the Greek word ‘dekas,’ which refers to a group of 10. A decade has different meanings, including;

- A period of ten consecutive years.
- A length of time (10years) that begins with a year whose last digit is 0 (zero)
- A series or group of ten

**How is the word decade used?**

As seen earlier, the word decade means ten years and has several uses. For example, we can talk of a person ‘first decade’ to mean the period from their birth to their tenth birthday and the second decade to mean the period between the 11^{th} birthday until one gets to twenty years. It is also possible to talk of a person’s last decade to refer to their last ten years on earth without necessarily encompassing any calendar years.

You can describe one’s age by referencing the tens digit. For example, two decades mean 20 years, three decades mean 30 years, four decades mean 40 years, five decades mean 50 years, etc.

**Which is the standard method for denominating decades?**

**There are two methods commonly used to express decades, namely;**

**0 to 9 decade**

In this method, which is the most common, decades are usually denominated by grouping years that share ten digits. This period includes years starting with 0 to one ending in 9. For example, the period starting from 1970 to 1979 is referred to as the 1970s, and that between 1980 and 1989 is known as the 1980s.

When using this method, people usually mention the tens part. For example, we can talk of the seventies or 70s and the eighties or 80s. But, this method of using only the tens can be ambiguous since it does not show the century that this period occurs. While this way of grouping years can be reliable and is common, it cannot apply to decades before A.D. 10 since the year 0 was not there.

**1 to 0 decade**

Although a rare method, it is also possible to group years from one ending in 1 to that ending in 0. In this procedure, the grouping of years is from the beginning of the era in the A.D. calendar, which helps to come up with successive decades. For example, the years 1 to 10 refer to the first decade, 11 to 20 second decade, 21 to 30 the third decade, etc.

When using this method, one needs to describe a decade using the century (100 years) in which it occurs. For example, you can talk of the 1^{st} decade in the 20^{th} century, the 3^{rd} decade of the 21^{st} century, the last decade of the 19^{th} century, etc. It is also possible to group the decades explicitly using this method. For example, 1971 – 1980, 1981 – 1990, 2001 – 2010, 2021 – 2030, and so on.

**Which are the other ways for grouping years?**

Besides using decades (groups of 10 years), there are other ways for grouping years, including;

**Centuries**

A century means 100 years. The word century (abbreviated as c) is derived from the Latin word *centum*, which means 100. People use abbreviations such as A.D. (Anno Domini) when naming years. Anno Domini is a system for abbreviating years and its Latin meaning ‘in the year of our Lord .’Years are also abbreviated using B.C., referring to ‘Before Christ.’

Recently, the abbreviations B.C.E. (Before the Common Era) and C.E. (Common Era) have been used to express eras. These terms represent the same periods as B.C. and A.D. minus the Christian reference. In this system, time is counted backward B.C.E. (Before the Common Era) and forwards C.E. (in the Common Era).

**Millennia**

A millennium is 1000 years, and the word is derived from the Latin word *mille*, meaning thousand. This period is calculated from the date of Christ’s birth.

**How many months are in a decade?**

A decade refers to a period of ten years. Since a year has 12 months, then one decade has 120 months. You can obtain this number by multiplying the number of months by years, i.e., 12 x 10 = 120 months. Using this multiplying factor, converting any number of decades to months is possible. For example;

1 decade = 120 months (10 x 12)

2 decades = 240 months (10 x 24)

3 decades = 360 months (10 x 36)

4 decades = 480 months (10 x 48)

5 decades = 600 months (10 x 60)

It is also possible to convert months to decades. To do this, you will first convert them to years then to decades. For example,

120 months = 1 decade (120/12 = 10, 10/10 = 1)

240 months = 2 decades (240/12 = 20, 20/10 = 2)

360 months = 3 decades (360/12 = 30, 30/10 = 3)

480 months = 4 decades (480/12 = 40, 40/10 = 4)

600 months = 5 decades (600/12=50, 50/10 = 5)

**How many days are in one decade?**

In order for you to calculate the number of days in a decade, it is important to first convert the decades into years and then to days. The number of days in a year is 365 in a standard year or 366 days in a leap year. For example;

1 decade = 3,650 or 3,660 days (1×10 x365 = 3,650 or 1x 10 x 366 = 3,660)

2 decades = 7,300 or 7,320 days (2 x 10 x 365 = 7,300 or 2 x 10 x 366 = 7,320)

3 decades = 10,950 or 10,980 days (3 x 10 x 365 = 10,950 or 3 x 10 x 366)

4 decades = 14,600 or 14,640 days (4 x 10 x 365 = 14,600 or 4 x 10 x 366 = 14,640)

5 decades = 18,250 or 18,300 days (5 x 10 x 365 = 18, 250 0r 5 x 10 x 366 = 18,300

It is also easy to convert a given number of days to decades by reversing the above process. To do this, one needs to first convert days to years then years to decades. For example;

3,650 days = 1 decade (3,650/365 = 10, 10/10 = 1)

5,475 days = 1 ½ decade (5,475/365 = 15, 15/10 = 1.5)

7300 days = 2 decades (7300/365 = 20, 20/10 = 2)

9,125 days = 2 ½ decades (9,125/365 = 25, 25/10 = 2.5)

**Key points and highlights**

The word decade comes from the Greek word *dekas, *referring to a group of ten*. *One decade is equivalent to ten years, and to get the number of decades in a year, we divide 1/10 = 0.1 decades. It also means 0.2 decades in 2 years, 0.3 decades in 3 years, 0.5 decades in 5 years, etc.

It is also possible to convert any number of decades to years by multiplying them by 10.

https://en.wikipedia.org/wiki/Decade

https://www.cuemath.com/questions/how-many-years-is-a-decade-a-century/