UnWire.HK placed the protector over the top of the 4.3 inch screen on the Samsung Galaxy S II and while the width was a perfect match, the screen protector for the Galaxy S III was a bit too big. When the protector was placed over the 4.65 inch screen of the Samsung GALAXY Nexus, it was still a bit too big which seems to confirm the rumored 4.8 inch display for the highly anticipated device.
Remember when the 4.3 inch HTC HD2 was considered to be massive? Now a 4 inch screen seems to be the smallest that many will accept. If the Samsung Galaxy S III does have a 4.8 inch screen, it fits perfectly halfway between the previous model and the 5.3 inch display on the Samsung GALAXY Note.
source: UnWire.HK (translated), PocketDroid via Phandroid
The USG screen protector was made just for the Samsung Galaxy S III and is larger than the 4.3 inch screen on the Samung Galaxy S II (R)