What is a standard large envelope commonly referred to as?

The term "No. 10" refers specifically to a commonly used size of envelope that measures 4 1/8 inches by 9 1/2 inches. It is standard for business correspondence and is designed to fit a sheet of letter-sized paper folded into thirds. This size is widely recognized in the postal and business community, making it an ideal choice for sending official documents, letters, and invoices. Its prevalence in office settings is due to its compatibility with standard letterhead, making it convenient and efficient for everyday communications.

The other envelope sizes listed do not reflect the standard naming conventions or dimensions recognized in professional correspondence. For instance, "Standard 12," "Business 8," and "Size B" do not correspond to common envelope classifications, leading to confusion in identifying the appropriate envelope type for specific business uses. Recognizing No. 10 as the standard large envelope is crucial for effective and professional communication.