Fuji quotes it as 118x163mm (they sell half plate Acros, just got some).
I looked at it, but I wasn't sure it'd fit my holders I won (purely by accident, honest!) on an auction site. Figured 18x24 film or paper would be possible to cut into two nice parts, so I'll start with some Agfa MCP I got in the closet.
“Do your work, then step back. The only path to serenity.” - Lao Tzu