Weeks numbering varies in different countries.
The weeks of the year in a Gregorian calendar are numbered from week 1 to week 52 or 53, depending on several varying factors. Most years have 52 weeks, but if the year starts on a Thursday or is a leap year that starts on a Wednesday, that particular year will have 53 numbered weeks.
The most common week numbering system is the International Standard ISO 8601, where Monday is the first day of the week followed by Tuesday, Wednesday, Thursday, Friday, Saturday, and with Sunday as the seventh and final day.
Click here to see what week of the year it is.