Advent calendar has 24 windows to open, one for every day until Christmas, as well as a red envelope to mail it (extra postage required). An Advent calendar is a very special calendar used to countdown to December 25: The celebration of the birth of Jesus. The Advent calendar tradition supposedly dates back to the 1850s. Calendar measure approximately 9 1/2" W x 7 5/8" H; Envelope 10 1/8" W x 8 1/8" H. If this is the only item being ordered Please contact us about 1st class postage. Sale and seasonal items are FINAL SALES.