Use df -h
from the command line:
$ df -h -T -x tmpfs -x devtmpfs -x ecryptfs
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda3 ext4 38G 23G 14G 63% /
/dev/sda2 ext4 190M 12M 175M 7% /boot
/dev/sda1 vfat 99M 30M 70M 30% /boot/efi
/dev/sda4 ext4 542G 421G 121G 78% /home
/dev/mapper/luks-backups ext4 962G 639G 323G 67% /mnt/backup
In GNOME, right-click a mountpoint and choose "Properties" – or use the System Monitor:
In KDE, right-click a mountpoint and choose "Properties":
Or use a partition tool like GParted – it also shows information about not currently mounted partitions, but on the other hand, it cannot display anything about encrypted partitions: