Unusual Size For 1917 Postal Stationery Item?

Back to the OP question:

The envelope is a UPSS size 14.

The envelope appears to be either catalog number 2222 or 2223. Would need to know paper quality and watermark. 2004 catalog prices range from $1 to $750 used. Though, there is a note that the $850 one is not known with C/C. However, unlisted items are found every so often.

Which catalog are you using?

Catalog of the 20th Century Stamped Envelopes and Wrappers of the United States, 2004, United Postal Stationery Society (http://www.upss.org).

This was the latest version, until they mail out the 2011 version, which should be happening as we post.

I will correct my previous post. That $850 (which was a mint price) should be $750. All could be different when we see the new catalog.

Ah. I have their 19th century catalog. Need to pick up the 20th Cent. one at some point.

One standard size used in that era is known as "Size 10", also known as "Knife-85".
These are approx 117 mm x 90 mm.
It helps to measure in millemeters.
Is this 117x90?

Size 14 is 117mm by 90mm, though individual envelopes can vary by a mm or two.

Sales of UPSS publications: http://www.upss.org/code/publications.php

Of general interest would be:
19th Century Envelopes
20th/21st Century Envelopes (just published)
Postal Cards

There are even catalogs devoted just to knives.

The bimonthly journal is quite good. Members have access to all issues back to 1948. Consider joining if you are into postal stationery.