The shopping cart in the March 6, 2011 comic (the previous strip) was a little large. Most carts in the US are 3'2” to 3'6” at the handle. This one is about 3'9”.
If you ask Ace, he'll say he's 6'1”, but that's maybe if he stands up straight and does some stretching exercises.
I've often said Rocky was 6'3”, but she's obviously 6'4”. She used to be a full head taller than Ace, when he was still 18, so maybe Luna's got another inch or two of growth coming.
At 5'7”, Carly is actually at the average height of a Japanese man.
Jaz is about 5'4” and right at the average height for an American woman.
Poor Luna doesn't even hit 5'. No wonder she likes heels.