Catalog envelope sizes
Use larger envelopes when folding would hurt the piece more than the extra postage or stock cost.
The usual flat-mail starting point.
Better once the stack gets thick or awkward.
Presentation pieces look cleaner when left flat.
Quick check
When to go bigger
If the insert is a kit, certificate, brochure, or presentation packet, flat handling usually beats forcing a fold. Larger envelopes also reduce the risk of dog-eared edges during packing.
- 6 x 9 works for compact booklets and smaller flat inserts.
- 9 x 12 is the common safe choice for standard flat document work.
- 10 x 13 gives you more breathing room when the packet has multiple pieces or heavier stock.
Larger envelope formats (in / mm)
| Size name | Common name | Item size | Shape | Best use |
|---|---|---|---|---|
| 6 x 9 | Booklet envelope | 6 x 9 in (152 x 229 mm) | Envelope | booklets, folded kits, manuals |
| 9 x 12 | Catalog envelope | 9 x 12 in (229 x 305 mm) | Envelope | flat documents and presentation sheets |
| 10 x 13 | Catalog envelope | 10 x 13 in (254 x 330 mm) | Envelope | larger packets and document sets |
Flat mail looks better when the contents slide in without wrestling. A too-tight larger envelope defeats the whole point.
Common questions
What envelope should I use for flat documents?
9 x 12 is the usual starting point. If the packet is thick or includes multiple inserts, 10 x 13 gives you more room and a cleaner close.
Is 6 x 9 too small for brochures?
Not always. It works for compact pieces, but the real question is whether the finished insert slides in without corner damage.
Why not just fold everything into a #10?
Because some pieces lose impact once folded, and some stock shows fold lines badly. Flat mail costs more, but it often looks better.