From LQWiki

Stat displays the status of a file or the filesystem a file is on.

To obtain information about a file:

$ stat file

To obtain information about the filesystem file is on:

$ stat -f file

Use the -c option and various format sequences to obtain tailored output or the -t format for terse (and easily parsed) output. See the stat man page for full details.

Find out the size

You can use stat to find out a partition's size in blocks. To find out a partition's size in bytes, use fdisk as described here.