Quote Originally Posted by Ikki View Post
Medium damage applied =
Display Attack Power × (1+ Assault Value + Character UP Imangeous Effect + Attack Buff + Assist)
× (1+ attribute value + weak point correction + attribute UP gestural effect + attribute buff)
× (1+ special attack)
× (1 + ally attack debuff)
× (1+ union protective guardian correction)
× (1+ other buff correction)
÷ {enemy defense × (1 + enemy defense correction)}

This was taken from the translated wiki thats why the english is weird, but you should get a pretty good estimate if you consider all the factors in that formula, enemy defense is usually 12 (i dont remember quite well but it was around this, if some1 can correct me thats cool), some bosses have more (light disaster) or less (wind disasters).
Ah, the 'divide 12' was basically what I was looking for. Wanted to incorporate my damage range onto my weapon skill spreadsheet but might be a bit of a hassle if there are various defenses.