You may have noticed that those Brits seem to love to talk about trim sizes in a totally weird way.  Rather than saying 5½” x 8½” they will come out with the outrageous Demy Octavo (which, even worse, they may write Demy 8vo). Note also that if you ever do pin them down to precise measurements they will talk in millimeters and give the dimensions the opposite way round than we do.  Thus a 6” x 9” book will turn into a 228 x 152mm one — if you’re lucky enough not to get bogged down in Medium 8vo.  This back-to-front dimension problem simply has to be accepted as part of the scenery, just as in the old days was the fact that they would always want was negs with emulsion down and we’d want them emulsion up (or was it the other way round?).  Knowing all this does help in dealing with Chinese printers – Hong Kong, Empire, it all makes sense.

The Demy 8vo story goes back to the early days of printing, and relates to the standard sheet sizes used 300 or 400 years ago.  So starting with a demy sheet, which measured 22½” x 17½”, folding it once will give you demy folio; fold it in half again and you’ve got demy quarto, again and it’s demy octavo, 8¾” x 5-5/8”.  Trim 1/8” off top & bottom and the fore-edge and you have a finished book trim size 5½” x 8½”.  Of course, even in the world of sheet-fed printing almost nobody has printed on a demy sheet for aeons: but in the middle of the last century Double and Quad Demy were not uncommon.

Here are a few of the old sheet/press sizes:

Double Quad Crown:  60” x 40”

Quad Demy:  45” x 35”

Super Royal: 27½” x 20½”

Royal: 25” x 20”

Medium: 23” x 18”

Demy: 22½” x 17½”

Music Demy: 20” x 15½”

Crown: 20” x 15”