I've just looked in the `i3status` manual to see how to display the free memory (as reported by `free`), and found no option.
I understand from the manual that computing the used memory is not easy, but displaying the total used or free memory (both RAM and swap) as reported by `free` is quite easy and useful. My particular usecase is this: I use quite a few of `tmpfs` instances mounted for various development purposes, which consume quite a lot of memory (in terms of GiB) and which spill over to swap (sometimes leaving me without any memory RAM or swap), and I would like to easily find out when I'm close to "out-of-memory". Looking through the i3 mailing list archive I found other usecases of such a feature: * `[i3] memory information in i3status` from 1st of April 2015, which talks about many processes chewing RAM; * `[i3] memory display` from 15th November 2014, which talks about image processing applications; There even seems to be a rejected patch implementing this in `[i3] [RFC] [PATCH] i3status: memory-stats` from 23th February 2012, or `[i3] [PATCH] i3status: implements a memory-usage-print` from the same day. Thus although the average desktop user never runs out of memory (either he has enough these days or uses swap), there are people -- especially developers or those using memory intensive applications like scientific or image processing -- that easily overrun both their RAM an swap. For example I have on my laptop 8 GiB RAM and a 32 GiB swap, and I'm constantly running out of available memory due to the mentioned `tmpfs` instances. Thanks, Ciprian.
