Much like how Kyrpton in the comics is far larger than earth which is why Superman is stronger than humans
one example is that despite living in a Feudal japan each Ninja village is pretty large large enough that by the fourth ninja world war there were over 80,000 shinobi that went to war. and there was still alot of people living in the villages.
another stronger evidence is at how fast the shinobi travel when running from one village to another while on mission
when they get missions you see them meet at the village entrance and when they are all ready they disappear as if they are moving at blindingly fast speed then you see them traveling at what appears to be a normal human sprint but the thing is they are not moving that slow they are moving as fast as they were when they started ie to the naked human eye they would be moving at blinding speed
at the bottom end such speed would be a couple hundred miles per hour Atleast
it has been said that it takes 3 day to go from the leaf to the sand village if they run for 12 hours a day that would mean that the leaf and the sand village are 7,200 miles away from each other and thats if they are running only at a couple hundred miles per hour my belief that they are actually moving at several hundred miles per hour neji stated in the flash back 2nd chunin exam that shinobi can move at super sonic speed this means that if they are moving as fast as super sonic or 760 mph
and it takes them 3 days of 12 hours to run to the village it would mean that the leaf and sand are 27,360 miles apart being that this is supposed to be all in a feudal japan this would mean that inverse japan alone is larger than our planet since earth is roughly 24,901 miles around
so what do you think do you guys think that the earth in naruto is larger than our earth based on the fact that these shinobi are actually moving at blinding speed yet it still takes 3 days for them to get to somewhere like the leaf