noun
standard-size mail
Refers to mail that meets the size and weight standards for regular postage, as opposed to non-standard or oversized mail.
定形郵便物の最大サイズは、長辺23.5cm、短辺12cmです。
The maximum size for standard-size mail is 23.5 cm long and 12 cm wide.
この封筒
Can this envelope be sent as standard-size mail?