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The limiting factor for desk depth for me is the distance from my eyes to the screen(s), once that is set the I need my hands to be in a suitable position on the keyboard (with enough desk before the keyboard for my wrists to rest on).
Just checking current setup my eyes are 70cm from my screens (dual 23" monitors).
The monitors are mounted on an arm that clamps onto the desk, this puts them about 10-15cm onto the desk.
Here's what it looks like (this is a 70cm deep desk):-
https://www.greenbank.org/misc/newdesk5.jpg
I could probably lose 5cm from the desk and still just about be ok.
So, in theory, if I mounted the monitors flush with the edge of the back desk I could lose a further 5cm-10cm of desk depth. So a 50cm deep desk would really be the absolute limit.
But I'm going to be upgrading to a single 43" 4K monitor at some point (when they become available for under £450) so I need to have the 70cm of desk there in case I need all of it.
As for height, it's a sit/stand desk and I've been keeping an eye on where I end up with the height when I move it back down. It's almost always on 80cm (measured floor to top of desk surface) although this will mostly be a factor of the stool I use to sit on. With the stool at its lowest the desk needs to be 80cm for my forearms to be horizontal between elbows and wrist. With the stool like this my feet and nicely planted on the floor and my legs just angling down from bottom to knees (like all of the classic office ergonomics pictures). I'm 5'8".
With a lower seat I could probably get away with a lower desk but much lower and it might encourage me to straighten my legs (which leads to a slouchy back) rather than having my feet planted on the floor.
Flexispot EC1 goes down to 73.5cm (including 2.5cm worktop).
tl;dr I'd probably say 60cm deep and 75cm high would be my minimum.
Can I check minimum desk depth and height?
I'm guessing 70 deep and 70 high should give plenty of room?