As in, how is the damage you take based on the monsters you fight and the armour you're wearing? (And how does the defense stat on your armour actually translate to a solid number?)
If anyone has the actual formula for damage taken that'd be pretty cool but considering I can't find it on the wiki under the page called "Damage" then I'm not sure anyone knows it
https://wiki.spiralknights.com/Defense
The Defense page is a bit more of what you're interested in, instead of the Damage page.
No one has come to the specific defense value, because it takes a ton of time to do.
https://forums.spiralknights.com/en/node/97633#comment-983369
I did it once for D13 and D23 guild hall training bags. All my values are in the proto sword link from my 97633 thread.
Zeddy placed a handful of estimations on the wiki page. They're good enough if you don't mind about a 3% error in damage.
As for the equation... this formula was presented. As mentioned in the Defense wiki page, when damage is large enough... it becomes a linear equation.
https://forums.spiralknights.com/en/node/97633#comment-884832
It passed Zeddy's tests. As for small attacks, I think I'm the only one that tested (and confirmed through that limited test) anything.