He's at least 4 inches, closer to 5 by now. He was smaller when we got him but he's grown a lot.
He's what was labeled as a Giant Halfmoon, he seems to be bigger then the regular Giant we got, but the regular one is still pretty new. Our smaller king would be fine in a 5 gallon tank but we have them both in 10 gallons, so they have more room. Elvis would be to big for a 5 gallon, he's pretty huge.
We've only ever seen 2 Giant Halfmoon bettas at petco - the other one we bought and it died within a few days. The cup was entirely to small for him and the lady said he actually came in not looking to good. http://www.bettafish.com/showthread....ighlight=lucky
I wanted him to live so badly, I completely fell in love with him and his color. Was heartbroken completely after he died.