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US Catalog Envelope
North America — primarily the United States and Canada — relies on a dedicated numeric sizing system for "catalog" envelopes that sets them apart from both global ISO standards and the social announcement formats. While announcement envelopes serve invitations and greeting cards, and commercial envelopes (like No. 10) handle folded business letters, catalog envelopes occupy the heavy-duty mailing niche. These envelopes are specifically engineered to send documents, booklets, and publications flat and unfolded, ensuring that reports, magazines, and marketing materials arrive crisp and professional without creases or bends.
Main Characteristic
Unlike commercial envelopes designed for tri-folded letters, and unlike booklet envelopes that open along their longer side, catalog envelopes are defined as "open-end" envelopes: the opening and gummed flap are located on the shorter dimension. This top-opening construction, combined with a sturdy center seam and heavier paper stock, makes them ideal for stuffing thick, multi-page contents and for high-volume automated insertion. The system features a more elongated, portrait-oriented aspect ratio that accommodates standard US paper sizes lying completely flat, prioritizing durability and protection over the aesthetic proportions of social stationery.
Measurement System
Everyday sizes: The core US catalog envelopes are named using a numeric system — such as 1, 6, 9¾, 10½, and 13½ — where the numbers traditionally represent a progression in size scale rather than any precise mathematical formula. It is crucial to note that these numbers have no relation to commercial envelope numbers (like No. 10) or to international ISO sizes. A higher catalog number simply indicates a larger envelope. The 10½ catalog envelope (9 x 12 in) serves as the undisputed industry standard for mailing unfolded US Letter-sized documents.
The Flat-Mailing Logic: The numbering system is built around holding standard US paper sizes without folding. For instance, a 10½ envelope (9 x 12 in) provides just enough clearance around an 8.5 x 11 in sheet to insert a thick stack of pages, while the larger 13½ envelope (10 x 13 in) accommodates documents inside a protective sleeve or a stack heavy enough to require extra room.
Common Usage:
- No. 10½: The dominant standard for mailing unfolded US Letter (8.5 x 11 in) documents, multi-page reports, contracts, and brochures. It perfectly accommodates a flat letter-sized sheet plus a substantial number of additional pages.
- No. 1: A smaller catalog format (6 x 9 in) used for half-letter documents, small booklets, photo prints, and compact promotional mailers that benefit from a flat, unfolded presentation.
- No. 6: Frequently used for medium-sized publications, mid-length reports, and booklets measuring up to roughly 7.5 x 10.5 in that are too thick or too important to fold.
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No. 9¾ / No. 13½: Larger formats reserved for oversized documents, bound presentations, magazines, catalogs, and bulky multi-page mailings that must remain flat and protected during transit.