How is resistance percentage calculated?

My character's resistance is listed on the details pane when I open my inventory, and it's a simple integer. It appears to undergo some type of calculation to determine the percentage of damage each of these actually counts for:

Judging by the tooltip, there's some factor based on enemy (and/or my?) level. I believe these numbers are 80 due to my intelligence - I had 798 at the time this was taken.

How is percentage resistance calculated? Although the base "Resistance" integer appears to be derived directly from my stats, does the percentage in this tooltip take into account skills, enchantments, or other modifiers that change resistance?

From Diablo 3 Formula List

Elemental damage reduction = Resistance / (5 × Monster Level + Resistance)

Just a quick sanity check on your example, since your level is 34 (thus it assumes your going up against level 34 monsters):

r = 80 / (5 * 34 + 80)
r = 0.32

(I imagine the 0.07% error is due to rounding on their side)

What can we learn from this?

The higher your level, the more resistance you need to achieve the same reduction in damage

and

Each point of resistance goes further at a lower level than a higher one.

E.g. at level 60;

r = 80 / (5 * 60 + 80)
r = 0.21

Sources of Resistance

Resistance from Intelligence:

resistance = int * 0.1

There is also flat +resistance on gear (As +Resist All or +Resist Element)

Resist - % Reduction @ Monster Level  
   MLVL ->    60      61      62      63  
   100      25.0%   24.7%   24.4%   24.1%  
   200      40.0%   39.6%   39.2%   38.8%  
   300      50.0%   49.6%   49.2%   48.8%  
   400      57.1%   56.7%   56.3%   55.9%  
   500      62.5%   62.1%   61.7%   61.3%  
   600      66.7%   66.3%   65.9%   65.6%  
   700      70.0%   69.7%   69.3%   69.0%  
   800      72.7%   72.4%   72.1%   71.7%  
   900      75.0%   74.7%   74.4%   74.1%  
   1000     76.9%   76.6%   76.3%   76.0%  
   1100     78.6%   78.3%   78.0%   77.7%  
   1200     80.0%   79.7%   79.5%   79.2%  
   1300     81.3%   81.0%   80.7%   80.5%  
   1400     82.4%   82.1%   81.9%   81.6%  
   1500     83.3%   83.1%   82.9%   82.6%  
   1600     84.2%   84.0%   83.8%   83.6%  
   1700     85.0%   84.8%   84.6%   84.4%  
   1800     85.7%   85.5%   85.3%   85.1%

This answer is actually directed at this question, but as it is closed as exact duplicate I will post it here.

Here is a list with the maximal possible resistances per slot (All Resistance / X Resistance (e.g. Arcane Resistance)):

• Max per gearset: 930 / 690

• gear slots: 12 / 12

• Shield: 80 / 60
• Amulet: 70 / 50
• Ring: 70 / 50
• Belt: 80 / 60
• Boots: 80 / 60
• Bracer: 80 / 60
• Chest: 80 / 60
• Gloves: 80 / 60
• Helm: 80 / 60
• Pants: 80 / 60
• Shldr: 80 / 60
• Cloak: 70 / 50
• Mighty Belt: 70 / 50
• Spirit Stone: 70 / 50
• Voodoo Mask: 70 / 50
• Wizard hat: 70 / 50

This list does not include legendaries and other skills / abilities. Generally speaking you can reach 930 All Reistance and add another 690 of a specific resistance for a total of 1620. This translates into about 83-85% damage reduction in Inferno, see: how is resistance percentage calculated

Source