test_as.rb

require 'active_support/core_ext/string/multibyte'
require 'objspace'

# load unicode database
''.mb_chars.upcase

db = ActiveSupport::Multibyte::Unicode.send(:database)
db_memsize = db.instance_variables.map do |ivar|
  ObjectSpace.memsize_of(db.instance_variable_get(ivar))
end.inject(:+)

puts "db_memsize: #{db_memsize} Bytes"
#=> db_memsize: 1501184 Bytes

test_ruby.rb

require 'objspace'

# load unicode database
''.unicode_normalize

db_memsize = UnicodeNormalize.constants.map do |const|
  ObjectSpace.memsize_of(UnicodeNormalize.const_get(const))
end.inject(:+)

puts "db_memsize: #{db_memsize} Bytes"
#=> db_memsize: 404558 Bytes