That depends what you use to measure.

At first I used RES column from FreeBSD top(1) command.

Here are results for the same desktop environments from other tools:

                | htop(1) | conky(1) | freecolor(1)
    ------------+---------+----------+-------------
        FreeBSD |  112 MB |    - -   |  157 MB 
        Openbox |  237 MB |  460 MB  |  382 MB 
           MATE |  508 MB |  778 MB  |  788 MB 
           XFCE |  533 MB |  794 MB  |  829 MB 
    helloSystem |  585 MB |    - -   |  830 MB 
          GNOME |  625 MB |  990 MB  | 1000 MB 
     KDE/Plasma |  730 MB | 1659 MB  | 1167 MB

This table above is also at the end of the blog post.

So as You see depending on the used tool you may get REALLY different results while having the same components started.

Regards.