The difference between catalog envelopes and booklet envelopes is that catalog envelopes open on the short side, while booklet envelopes open on the long side.
Number		Envelope Sizes		Recommended Enclosure Dimensions*
3 Booklet		61/2 x 43/4		6 x 41/2
5 Booklet		81/8 x 51/2		75/8 x 51/4
6 Booklet		87/8 x 53/4		83/8 x 51/2
61/2 Booklet (#1 Catalog)		9 x 6		81/2 x 53/4
63/4 Booklet (#11/2 Catalog)		91/2 x 61/2		9 x 61/4
71/4 Booklet (#3 Catalog)		10 x 7		91/2 x 63/4
71/2 Booklet (#6 Catalog)		101/2 x 71/2		10 x 71/4
#93/4 Catalog		111/4 x 83/4		11 x 81/2
9 Booklet		111/2 x 83/4		11 x 81/2
91/2 Booklet (#101/2 Catalog)		12 x 9		111/2 x 83/4
#121/2 Catalog		121/2 x 91/2		12 x 91/4
10 Booklet		125/8 x 91/2		121/8 x 91/4
13 Booklet (#131/2 Catalog)		13 x 10		121/2 x 93/4
#141/2 Catalog		141/2 x 111/2		14 x 111/4
#15 Catalog		15 x 10		141/2 x 93/4
#151/2 Catalog		15 x 12		141/2 x 113/4

 Denotes that an InDesign CS (Version 3) template may be downloaded
*Note: If the enclosure is unusually bulky, the envelope may need to be the next larger standard size.