Get week from Specific date

DateTime date = DateTime.Now;

System.Globalization.CultureInfo cult_info = System.Globalization.CultureInfo.CreateSpecificCulture("no");

System.Globalization.Calendar cal = cult_info.Calendar;

int weekNo = cal.GetWeekOfYear(date, cult_info.DateTimeFormat.CalendarWeekRule, cult_info.DateTimeFormat.FirstDayOfWeek);