Get to the command line/terminal

Open a new command line/terminal session.

If you're using Jessie Lite, this is the default state that your Pi boots into.

If you're using RetroPie, you can get here by pressing F4 on a keyboard or by exiting to the command line through the RetroPie UI.

If you're using Raspbian Jessie PIXEL (desktop), simply open a new Terminal.

Run the following command

Run the following command and press enter:

df

This will display the total disk usage for your SD card in columns. If you'd like to make it more readable, you can add the -h flag, which will add G and M units for gigabytes and megabytes:

df -h