In Mac OS X, the default size is 48x48. But you can resize it to anything you want.
If you want it to look like the default icon size, do the following:
Right-Click on your Desktop and press Properties.
Click the Apperance tab, then Advanced. In the drop-down box "Item", select "Icon". Then, to the right you should see a two numbers like "32x32" or "16x16". Change both of them to 48x48.
I'm wirting this by memory since it might not be 100% accurate.
Well actually, do what Nylock says, but you can't set it to 48x48. You have to change the size to something around 64, also you should see this thread: Mac OS X Icon Spacing and Size
i'm french and my language is not good 
Linear Mode
Main Menu