It currently shows in GB, MB which are multiples of 10. I'd like it to be multiples of 2.
You can't do so, mainly because Ubuntu follows the Units Policy.
If user expect to see file sizes in base-2 using the default file manager in Ubuntu, forget about it. Most known file managers have been using base-10 for some time already.
File managers that show base-10 a.k.a Metric units (kB, MB, GB):
- Nautilus (GNOME, Unity)^1
- Caja (MATE; Ubuntu MATE)^3
- Thunar (Xfce; Xubuntu)
- Nemo (Cinnamon)^3
While the policy applies to default file manager in Ubuntu for 10.10 and newer releases, there are file managers that did not follow the same.
File managers that show base-2 a.k.a. IEC units (KiB, MiB, GiB):
- Dolphin (KDE; Kubuntu)^2
- PCManFM (LXDE, LXQt; Lubuntu)^3
- Double Commander (cross-platform)
^1: Nautilus in Ubuntu 10.10+ will now show base-10; previously base-2.
^2: Dolphin will show either base-2 or base-10 in KDE Plasma 4; otherwise always base-2 in KDE Plasma 5. Some details at below.
^3: The file manager has an option to show either base-10 or base-2.
Notice that file managers that show file sizes in base-2 are often found as platform independent software. This may be influenced by the fact that operating system for consumers, esp. Microsoft Windows, use customary binary prefixes a.k.a. JEDEC units.
As for Dolphin file manager, it is the KDE development platform that allows its application programs to show file sizes in base-2, rather than the file manager itself. Such option has been available in KDE Plasma 4, but went missing in KDE Plasma 5.
We can trace back the history, when the blueprint was registered in late-2008 by Joel Parker. Two years later, the policy was finally implemented in Ubuntu 10.10. For such carefully planned changes, it is very less likely for file manager in Ubuntu to revert the changes. Time will tell.
TL;DR Use a file manager that show file sizes in base-2 (KiB, MiB, GiB) for consistent experience across different operating systems. Very less likely for base-2 to be reintroduced in Ubuntu anyway.
I use Thunar 1.8.15 and it has an option to show either base-10 or base-2 (
Show file size in binary format). Also see Xfce wiki.