Nautilus is the default file browser in Ubuntu. Nautilus by default doesn't shows the size of the file. But if you need to show the size of file in Ubuntu, a simple tweak to Nautilus will do the trick. Here we have listed the different steps required. Take a look.

• Open nautilus, that is simply open some folder say, home folder. The file browser thus props up is called nautilus.
• GOTO edit->preferences . A new window will open up.
• Now GOTO tab called Display.
• Their ,under the title, icon captions, you will see three options.
• Change the first option to size.
• Thats all. Now go and check the Nautilus file browser in Ubuntu. Files will be displayed with its size underneath.

Hope we have solved the issue. Please feel free to ask any questions in this regard.
Enjoy the free world :-)