Jupiter's diameter is 142,857 km, compared to Earth's petite
12,391 km, making Jupiter 11.52 times wider: if we take
at 185 cm and give him a relative Earth height to Jupiter's
he becomes only 16 cm tall. Or, just to be silly, we could
imagine a Jupiter Man of Niel's relative proportions walking
around Earth, who would be over 213 meters tall.)
However, Sender claimed to be the size of Great Britain,
which was a good guess, since he/she/it seems to be shaped
approximately like a 900 km long "flatworm"; about 200 km wide at
the "head" and tapering away to a few km at the "tail", being
roughly 80 km thick.
This is much greater than the relative size a Jupiterian "human"
should be, and even a Blue Whale at 30 meters would only measure
up to 3.5 km: Sender is proportionally 257 times larger
largest living creatures.