cPanel has a built in feature for checking your disk usage. In the left hand menu of cPanel it will display total disk usage of your limit, however if you require a breakdown of where the consumption lies cPanel provides this functionality through a special tool:

1. Login to cPanel.
2. Click the Disk Space Usage icon.
3. The page will now display a breakdown of your disk usage.

If you have a large number of files or a high disk consumption, the page may take some time to load.