How to know if you have a 32 bits or a 64 bits Linux kernel?

Want to install an application on your favorite Linux but you forgot if it a 32 bits or a 64 bits one and you don't know which package you have to download? Don't panic. Just type in a console :

file /sbin/init

This will check /sbin/init file type and you will see if it is a 32 bits or a 64 bits executable file. I tested it on Ubuntu 13.04 and CentOS 6.4.