What is a business size 10 envelope?

A business size 10 envelope is a commercial envelope that is 9.5 inches tall and 4.125 inches wide. It is commonly used for business, direct-mail and personal correspondence.

Also known as business or standard envelopes, commercial envelopes come in a variety of sizes. Most are designed to have an open side with a commercial-style flap and diagonal seams, though some have pointed or square flaps. They may contain single or double windows that allow the mailer's and receiver's addresses to show through the face of the envelope. These windows are a convenience for businesses that use them for invoices or billing statements, paychecks and receipts.