tl;dr
require 'objspace'
ObjectSpace.memsize_of([0] * 1_000_000)
#=> 8000040
ObjectSpace.memsize_of(Array.new([0] * 1_000_000))
#=> 40
require 'objspace'
ObjectSpace.memsizerequire 'objspace'
ObjectSpace.memsize_of([0] * 1_000_000)
#=> 8000040
ObjectSpace.memsize_of(Array.new([0] * 1_000_000))
#=> 40
require 'objspace'
ObjectSpace.memsize