Week

What Is Week?

A week is a unit of time that is equal to seven days in a row. People all over the world use weeks to plan school, work, sports, trips and many other activities. A week usually starts and ends on the same day every time, which makes it easy to follow a regular routine.

Definition

A week is a standard unit used to measure time.

• 1 week equals 7 days.
• 1 week equals 168 hours because 7 days times 24 hours per day equals 168 hours.
• 1 week is about 0.23 of a month because most months have around 30 or 31 days.
• 1 week is about 0.019 of a year because most years have 52 weeks and 1 day.

Most people think of a week as having seven named days in a fixed order, usually:

• Monday
• Tuesday
• Wednesday
• Thursday
• Friday
• Saturday
• Sunday

Some countries and religions count the first day differently. For example, many people in Europe treat Monday as the first day of the week, while many people in the United States and in some religions treat Sunday as the first day.

History / Origin

The idea of a seven day week is very old. It did not come from nature in the same way that a day comes from the rotation of the Earth or a year comes from the orbit of the Earth around the Sun. Instead, humans created the week to help organize life and religious practices.

Long ago, people in ancient Mesopotamia and nearby regions noticed seven special objects in the sky that they could see without tools. These were the Sun, the Moon and five visible planets. They chose the number seven as an important number and built calendars and weeks around it.

Later, the seven day week became part of Jewish and then Christian and Islamic traditions. In these faiths there is a regular rest or holy day each week. For example:

• In Judaism there is Shabbat, the day of rest, on Saturday.
• In Christianity Sunday is often a main day of worship.
• In Islam Friday is a special day for midday prayer.

The Roman Empire at first used an eight day market cycle. Over time, the Roman system changed and the seven day week spread across Europe. Through trade, religion and colonization, the seven day week became the common standard in most of the world.

Symbol & Abbreviation

There is no single official symbol for the week in the International System of Units, but people use some simple short forms in writing and maths.

• Common abbreviation: w or wk
• Plural: wks is sometimes used for weeks

Examples:

• 2 w means 2 weeks.
• 6 wk means 6 weeks.

Current Use Around the World

The seven day week is used in almost every country on Earth. It appears in calendars, school timetables, work schedules, TV guides, sports fixtures and many apps on phones and computers.

Some differences exist from place to place.

• First day of the week
  Many European countries and the international standard called ISO 8601 treat Monday as the first day of the week. In the United States and some other places, Sunday is seen as the first day.
• Work week and weekend
  In many countries people work from Monday to Friday and rest on Saturday and Sunday. In some countries, the main days off are Friday and Saturday, or Thursday and Friday. This work week pattern can change based on local laws and culture.
• School week
  Most schools have classes five days each week and two days off, but which days are used can be different in each country.

Digital systems and international organizations usually follow the ISO 8601 standard where weeks are numbered, and Monday is counted as day one of the week for clear communication across borders.

Example Conversions

Here are some useful conversions between weeks and other common time units.

Week to days and hours

Week to months and years

Because months and years are not all the same length, the numbers below are approximate.

• 1 week is about 0.23 month.
• 4 weeks is about 1 month, but a real calendar month usually has 30 or 31 days.
• 52 weeks is most of 1 year, but a year is 52 weeks and 1 day or 52 weeks and 2 days in a leap year.

Quick conversion rules

• To change weeks to days, multiply by 7. Example: 5 weeks times 7 equals 35 days.
• To change days to weeks, divide by 7. Example: 21 days divided by 7 equals 3 weeks.
• To change weeks to hours, multiply by 168. Example: 2 weeks times 168 equals 336 hours.

Related Units

The week is closely linked with other time units that people use every day.

• Second the base unit of time in science. All other time units can be written using seconds.
• Minute 60 seconds. There are 10,080 minutes in one week.
• Hour 60 minutes or 3,600 seconds. There are 168 hours in one week.
• Day 24 hours. There are 7 days in one week.
• Month usually 28 to 31 days. A rough rule is that 4 weeks is close to 1 month.
• Year about 365 days or 52 weeks and 1 day.

People sometimes talk about longer blocks made from weeks, such as:

• Fortnight a period of 2 weeks or 14 days.
• Quarter a period of 3 months. A quarter is about 13 weeks.

FAQs

Why does a week have seven days?

A week has seven days mainly because of history and tradition. Ancient peoples chose the number seven for religious and cultural reasons, linked with the seven visible heavenly bodies. Later religions and empires kept this pattern, and it became the normal standard worldwide.

Is a week a unit in the official SI system?

No, the week is not an official SI unit. The only base unit for time in the SI system is the second. However, weeks are widely accepted and used in daily life, business and many types of planning, so they are still very important.

Does every country start the week on the same day?

No, not every country starts the week on the same day. Many places, and the ISO 8601 international standard, say that Monday is the first day. Some other places, such as the United States, treat Sunday as the first day. Calendar apps often let you choose which day your week starts on.

How many weeks are in a year?

There are 52 full weeks in a year, plus 1 extra day in a normal year or 2 extra days in a leap year. This is why the exact number is often written as 52 weeks and some days instead of a simple whole number.

Is four weeks the same as one month?

Four weeks is 28 days, but most months have 30 or 31 days, and February has 28 or 29 days. So four weeks is close to a month but usually a little shorter. For careful planning, such as paying rent or interest, people use calendar months, not 4 week blocks.

What is a fortnight?

A fortnight is a word that means two weeks or 14 days. It is used more often in British and some other types of English. For example, someone might say, “I will see you in a fortnight” to mean “I will see you in two weeks.”

How do week numbers work?

In some calendars and in business, each week of the year is given a number, such as week 1, week 2 and so on. The ISO 8601 standard says that week 1 is the week that contains the first Thursday of the year, and that weeks start on Monday. This system helps companies and groups in different countries plan events and projects without confusion.

Why are weeks useful?

Weeks are useful because they are short enough to plan daily tasks but long enough to see patterns in work, school and rest. They help people set routines such as school days, work shifts, sports practice, homework time and family days off.