Aerogramme via airmail envelope size

An aerogramme is a special type of letter that is designed to be sent by airmail and is typically used for international correspondence. The size of an aerogramme is standardized by the Universal Postal Union (UPU) and is as follows:

Aerogrammes are designed to be folded and sealed, and they usually have a special adhesive strip along one edge to help keep them closed. They are typically made of a lightweight, thin paper that is designed to be lightweight and easy to mail.

It's worth noting that aerogrammes are not as commonly used as they once were, as email and other digital forms of communication have become more popular. However, they can still be a fun and unique way to send a letter or postcard to someone, especially if you want to add a personal touch or include a special message or photo.