Envelope Sizes

An envelope has to be bigger than its contents, and by a specific amount. The working minimum is 1/8 inch larger than the insert in both width and height. Below that the insert binds on the way in, corners catch on the seams, and an insertion machine jams.

For anything thicker than a couple of sheets, or for a card in a sleeve, give it 1/4 inch instead. The finder above uses 1/8 inch as the pass mark and flags the sizes that only just clear it.

Commercial envelopes are the business sizes, numbered: #9, #10, #11. The #10 at 4.125 x 9.5 in is the default business envelope in North America and takes a letter-size sheet folded in three.

Announcement envelopes are the A sizes. They are squarer, open on the long edge, and are what invitations, greeting cards and photos go in. 4OVER4 prints the A2 at 4.375 x 5.75 in and the A7 at 5.25 x 7.25 in, plus A4, A6, A8, A9 and A10, and square envelopes from 5 x 5 to 6.5 x 6.5 in. Note that an announcement A7 has nothing to do with the ISO A7 paper size.

The remittance envelope is the third family: a #9 Remittance at 7.5 x 8.875 in or a #6 3/4 Remittance at 6.5 x 7.125 in, with a deep flap that becomes the return envelope. Donation, offering and payment returns go in it.

USPS sorting equipment reads a rectangular piece whose length divided by its height falls between 1.3 and 2.5. Inside that band the mail runs through the machines at the machinable rate. Outside it, a square envelope being the usual culprit, the piece is pulled out and handled by hand and pays a nonmachinable surcharge.

The square envelopes on the chart, 5 x 5 to 6.5 x 6.5 in, fall outside that band. Pick a rectangular size if the mailing has to go at the machinable rate.