Approx 4" (100mm) diameter.
Unsure of the origins of this patch design: The first European to do a spacewalk was the French 'spationaute' Jean-Loup Chrétien, who flew to the Russian Mir space station in 1988. His sortie lasted six hours – a record at the time. The first spacewalk by an ESA astronaut was made by Thomas Reiter from Mir in 1995 in a Russian Orlan suit.
ESA's EVA patch worn on joint European/Russian missions from TM-20 onwards.