The dired-du Package

(unless (package-installed-p 'dired-du)
  (package-refresh-contents)
  (package-install 'dired-du))

(require 'dired-du)
;; (add-hook 'dired-mode-hook 'dired-du-mode)
(setq dired-du-size-format t)
(define-key dired-mode-map (kbd "K") 'dired-du-mode)