Smallest Full ATX case

[Vario]

This is indeed a smaller ATX-compatible case measured by volume. As a dual-chamber design, it's wider than many ATX cases but it's also far shorter than most.

ATX power supplies are out of the question with this case but it will accommodate SFX-L power supplies.

I own that very case O11 Air Mini {NOT THE O11 Dynamic Mini (only SFX PSU, but does fit 2x 360 rad?) and NOT the O11 AIR (that thing sucks)} and I have a massive honking 180mm PSU in it. (Leadex SE 1000 W Platinum) In terms of size, its bigger than my Lian Li PCA05NB which is a smaller midtower not sold anymore, otherwise would be perfect for OP probably. Don't confuse the O11 Dynamic Mini with the O11 Air Mini, they are very different.

Its a good case, but has some issues
First the good:
1) Very sturdy build quality, its all steel and glass with very minimal plastic. I like the look a lot.
2) The airflow is incredible, great temperatures, especially for an air cooled system. Really great temperatures. But probably not ideal for a watercooling setup because I don't think you can run a 360 rad, unless maybe a thin one at the roof with thin fans and you drilled some screw holes.
3) I can fit a giant power supply inside.
4) cable management is awesome.
5) I fit an E-ATX board inside
6) You can run a lot of 140mm fans, though the top makes sense to use 120s instead, I am using three of the Noctua NF-A12x15 thin fans for the top because there isn't much space at the top with my motherboard. Really should just run two but three looks better.
7) You can run a huge graphics card
8) the case IO (usb, etc) works well. it lacks a reset so I bought a power/reset PCI device and I can reach around and reset it there.

Second the bad:
1) its actually pretty big in terms of desk foot print, because its so wide. Its also heavy, but thats because its so sturdy, so not really a negative, just a commentary. It looks small from most angles but it actually takes up space like a regular midtower in reality.
2) HDD cage only fits two spinners, not an issue for me, I just slide one in at a time for backups and pull them after
3) Not good for watercooling, the top doesn't fit a 360 rad unless you found some way to modify it, I think best options you can do is a 280 front, 240 top, 240 bottom, 240 side?, could be wrong, haven't tried.
4) the HDD cage blocks the rear access the CPU cooler mounting area, so you have to remove motherboard to change heatsink/cpu. I made the HDD cage removable, but the CPU access hole doesn't even remotely line up to where my heatsink is so its worthless, still have to remove motherboard to change heatsink/cpu.
5) the bottom dust filter is pretty restrictive because it sits so low to the desk surface but I removed it so who cares
6) my videocard doesn't really fit that great, for some reason, the metal PCI slot tab doesn't fit well so sometimes I couldn't get it to slot into the case metal. Really dumb. It had to do with how the power supply's screws hold the panels together.

 

[phanbuey]

I have a mini non air and it's a big case... it's short, but not exactly 'small'.

 

[Bill_Bright]

Its also heavy

Surprised to see that since Lian Li is known for lightweight aluminum cases. But the review states, "Steel, aluminium, and tempered glass". Aluminum (or aluminium on that side of the big pond) is light. But steel and tempered glass are not.

 

[Vario]

Surprised to see that since Lian Li is known for lightweight aluminum cases. But the review states, "Steel, aluminium, and tempered glass". Aluminum (or aluminium on that side of the big pond) is light. But steel and tempered glass are not.

The Lian Li PC A05NB is really light, its aluminum like you say. I own four of them. However, modern Lian Li are heavy as fuck because they are steel based.

 

[cvaldes]

My bad, I'm confusing the various O11 cases.

I own the O11D Air (non mini version) which I am quite satisfied with. I consider this to be a smaller ATX-compatible case; it is much smaller by volume than the Lancool II Mesh Performance which I also own.

More than anything else, OP's budget will restrict what is available to him. I am not familiar with local market pricing and I don't know if any of the O11 models will comfortably fit in his budget.