3DS Max System Units for GZDoom/Scale of one unit in Doom?

[Thunderysteak]

TL;DR =
1 Doom Unit/Pixel is how many inches/millimeters?

I'm working on model prefabs for a Doom mod that are used for quick worldbuilding/reusability of assets/detailed stuff that are hard to create in Doombuilder alone, but there's a problem that I have no idea how large is one unit in GZDoom for models. So far I'm doing trial and error with crates and found out with a friend that one crate with the width of 10 inches is 8 units in GZDoom.

https://files.facepunch.com/forum/upload/209432/6051b758-7236-402e-b414-ede1d59d3766/image.png

https://files.facepunch.com/forum/upload/209432/388a7328-5eb8-4f7a-8dd0-6980527efe2c/image.png

Basically I want to set my 3DS Max system units to be compatible with GZDoom, so the dude that gives me the sketches what to model doesn't give me the scale in boxes but the proper units that Doom uses. For example the spikes he told me to make with the sketch that has the scale in the boxes:

https://files.facepunch.com/forum/upload/209432/e1012cbd-8077-4593-a61e-acfb03fa8615/image.png