Imperial (Paper)
Modern equivalent
30 × 22 in = 660 sq in = 762 × 559 mm
At 30 by 22 inches, the largest of the common traditional British sheets.
Imperial was the top of the ordinary range at 30 by 22 inches. Beyond it lay the sizes with the better names — elephant at 28 by 23, and double elephant and antiquarian above that — but imperial was the largest sheet in everyday commercial use.
It is also the one traditional British size still in active daily use, because watercolour paper is sold by it. A full imperial sheet is 30 by 22 inches, and half imperial and quarter imperial are standard in art shops that have otherwise gone entirely metric. A measure abolished for commerce can survive indefinitely in a craft, which is a pattern this archive records rather often.
The name has nothing to do with imperial weights and measures. It was a mill’s name for its largest standard sheet, in the same register as royal and crown, and it predates the 1824 Imperial system it now shares a word with.