pdf_size.rb

require 'pdf/reader'
require 'bigdecimal'

def pt2mm(pt)
  (pt2inch(pt) * BigDecimal.new("25.4")).round(2)
end

def pt2inch(pt)
  (pt / BigDecimal.new("72")).round(2)
end

reader = PDF::Reader.new(ARGV[0])
reader.pages.each do |page|
  mediabox = page.page_object[:MediaBox]
  width  = mediabox[2] - mediabox[0]
  height = mediabox[3] - mediabox[1]

  puts "Width : #{width}pts #{pt2mm(width).to_s}mm #{pt2inch(width).to_s}inch"
  puts "Height: #{height}pts #{pt2mm(height).to_s}mm #{pt2inch(height).to_s}inch"
end