At what size of tv does 720P start to look better than 480P?

I know that 1080P looks better than 720P at 50" and up.

But at what size of tv does 720P start to look better than 480P?

it looks better at any size

just like 1080p

you don't need 50"

1080p on a 20" screen will look better than 720p

it's all relative to how close you are sitting to it