The large 501st Legion patch has the same design as the regular patch, but is larger.
The round patch is about 10 cm. (4 in.) in diameter. This patch is 27 cm. (10,6 in.). I also have patches from Nordic Garrison and First Imperial Stormtrooper Detachment in this size.
Pictured here with a regular patch and a LEGO Tatooine Moisture Farmer’s Nephew minifig for scale.