The command to use is du, short for Disk Usage. It’s main purpose is to gather and summarize how much of your disk space is being used up by either files or directories in the Linux system.
Basic usage (with the -h switch to report back the size in easy to understand user friendly units) is:
du -h /home/craiglotter
This will recursively list all folders and their respective sizes as well as the total size of the selected folder in the appropriate size unit.
Adding the -s for summarize switch will return only the total file size for the selected directory (this is still recursive in case you were wondering).
du -sh /home/craiglotter
If you want the size for all files in the current directory also displayed, add an asterisk to your query. Similarly, if you want only files of a specific type listed with their respective sizes, modify the asterisk with the desired file extension.
du -sh /home/craiglotter *
du -sh /home/craiglotter *.txt