I got a better scale and magnifying glass. The 24.5mm is about as close as I can get but the badge is really about 0.97 inch.
I am measuring a naked metal badge, not the space where it goes.
This is the one that says "Personal Computer" in small italics under the large IBM logo. I think it came from an XT.
The plain one from a 122-key terminal looks to be about 25/32" or 19.5mm square.