### Week Numbering Systems

A *week* is a time unit equal to *seven days*.
Weeks within a given year are typically numbered *starting from 1*.
There are few week numbering systems used around the world.
USA, Canada, most of Latin America, Japan, Israel, South Korea, among
others, use a week numbering system (called *North American* in our
Calculator) in which the first week (numbered 1) of
any given year is the week which contains January 1st. The first day of a
week is Sunday and Saturday is the last.

Most of European and Asian countries use a standardized *ISO 8601 week date*
system in which the week with the number 1 is the first week which contains
*the first Thursday of January*.
In this system the first day of the week is Monday.
It may happen that the first week of the year contains a few last days from the
previous year. For example, the first week of the 2014 starts on December
30, 2013 (Monday) and ends on January 5, 2014 (Sunday).

Most Middle East countries use a calendar system (called *Islamic* in
our Calculator) in which the week with the number 1
in any given year is the one that contains January 1st. In this system
Saturday is the first day of a week and Friday is the last.

### How Many Weeks Are In a Year?

The short answer is 52 or 53 depending on a year number. Each year contains at least 52 weeks. A quick calculation confirms that 52 (weeks) times 7 days (per week) equals 364 days and there are 365 days in a year (366 in a leap year). Existence of the 53rd week depends on a year number and the week numbering system used. Detailed information on how to calculate the number of weeks in a year can be found, for example, on Wikipedia.

Our Week Number Calculator can be used as a convenient tool to quickly check week's number and dates in one of the three numbering systems. You can easily switch between the different week numbering systems using the select box.