How many "windows" does a traditional Advent calendar usually contain?

An Advent calendar is a special calendar used to count the days of Advent in anticipation of Christmas. Since the date of the First Sunday of Advent varies, falling between November 27 and December 3 inclusive, many Advent calendars, especially those that are reusable, often begin on December 1, although those that are produced for a specific year often include the last few days of November that are part of the liturgical season. The Advent calendar was first used by German Lutherans in the 19th and 20th centuries.

Many Advent calendars take the form of a large rectangular card with "windows", one for each day of December leading up to and including Christmas Eve (December 24) or Christmas Day (December 25). Consecutive doors are opened every day leading up to Christmas, beginning on the start of the Advent season for that year, or simply on December 1.

Often the doors are distributed across the calendar in no particular order. The calendar windows open to reveal an image, a poem, a portion of a story (such as the story of the Nativity of Jesus), or a small gift, such as a toy or a chocolate item. Often, each window has a Bible verse and Christian prayer printed on it, which Christians incorporate as part of their daily Advent devotions. Advent calendars may also have puzzles and games printed on their reverse side.