Same as res unless you have an item such as Tyrael’s Might, or an Elixir which can increase your max resist by a certain amount up to 85% (cap). Go into your Stats & Materials tab, scroll down to Resistances, if they’re green, they are maxed out, anymore won’t do any good. If they’re still a dull yellow color, you can still invest some into them.
Also if you hover over the resists on that character sheet, you can see how much over you are. For example my barb shows 70% Lightning Resist, but if I hover over it it shows:
You currently have 134.5% Lightning Resistance from bonuses and -50.0% from penalties (-14.5% away from your Maximum Lightning Resistance).
What this means is I’m actually 14.5% over the cap (note the negative sign in the tooltip). The cap in WT4 is 120% (-50% from just being in WT4) - again without items such as Tyrael’s Might or an elixir boosting your MAX higher.
Now my poison is actually not capped on my barb, so it shows:
You currently have 116.9% Poison Resistance from bonuses and -50.0% from pentalities (3.1% away from your Maximum Poison Resistance).
I need 3.1% more Poison resist to max it out, which is helpful, just as showing the -14.5% is helpful in telling me I’m slightly over the cap and it’s not doing me any good. Hovering over your Armor stat will do the same thing and let you know what the actual cap is 9230.