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Guide:Defense 101 v1.11, by Alecz

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Diablo II Strategy Guide Info:


There's much discussion about defense and its uses. Some players believe it is completely useless while others believe defense can be very helpful. From my online experience, I've found out that many people like to have high defense, but don't really know what defense does.

I do not claim to know a lot of things about the game, and I'm pretty sure for many of you here, this guide will not provide much new information, but since I couldn't find a rich source with information about defense, I decided to collect all that I found out and put it together in this guide. Some of the content is taken from other guides, while other is my own experience, testing, and speculation.

Note: I have little experience with assassin and Druid builds, so I will not refer to them very much.

Facts about defense

Does not reduce damage directly

Many of us know this. This is one of the "missing" features about defense in Diablo. No matter how much defense you have, when a monster hits you you will take the same damage.

Defense when running

While it's commonly said that defense = zero when running, this is not true. You are much more likely to be hit while running, but the actual game mechanism is that the entire to/hit formula is ignored, and that any attack that can hit will will deal damage.

The difference is that by ignoring the to/hit calculation, factors besides defense, such as Clvl and Mlvl, are ignored. Thus low level monsters that would often miss a naked high level character who was standing still, will usually hit that same character, if they are running (even if they have on heavy armor).

To benefit from defense you must walk, stand, or attack.

What Defense does


Defense reduces the chance that a physical attack that uses Attack Rating will be successful.

If you hover your mouse over the defense rating number you can see that chance as a %. This is being recalculated every time you hit a monster or a monster hits you. So if you want to see the % a zombie will hit you, just go and hit one, and the game will calculate it.

  • Some physical attacks are of the Ignore Target's Defense type (such as Smite and guided arrow), defense does not help against them.

Defense and special damage

Defense has no effect on elemental, poison, or magical attacks.

However if Skeleton archers shoot fire arrows at you, and the defense blocks the arrow, then you will not receive any fire damage.

How defense works

% Chance to/hit

The Chance to hit Formula with lots of examples:

The formula that calculates the chance to be hit is the following: (taken from Facts & Formulae Archive by Dracoy & Co)

  • Chance to be Hit = 100 * AR / (AR + DR) * 2 * alvl / (alvl + dlvl)

AR = Attack Rating; alvl = Level of Attacker; dlvl = Level of Defender; DR = Defense Rating

So for example, lets take a lvl 85 character and a Death Lord (mlvl 85). The character has 2000 defense, and the monster has 6134 AR (taken from arreat summit)

Chance to be Hit = 100 * 6134 / (6134 + 2000) * 2 * 85 / (85 + 85) = 75%

if you double your defense (say with lvl 1 shout or armor shrine) then the % to be hit becomes: Chance to be Hit = 100 * 6134 / (6134 + 4000) * 2 * 85 / (85 + 85) = 61%

As you can see double defense does not actually mean 1/2 chance to be hit.

If you level a bit more, and fight the same monster at lvl 90 with the same defense, the % to be hit becomes: Chance to be Hit = 100 * 6134 / (6134 + 2000) * 2 * 85 / (85 + 90) = 73%

Now if you double you defense the % to be hit becomes: Chance to be Hit = 100 * 6134 / (6134 + 4000) * 2 * 85 / (85 + 90) = 59%

So both character level, monster level, character defense, and monster's attack rating affect this chance considerably.

For the sake of argument, and because Act 2 defiance merc's are very popular let's see what that merc can do for us in the above scenario.

Act 2 defiance merc hired from Normal will give a boost of 240% (slvl 18 Defiance) at lvl 85 So the % to be hit becomes:

Chance to be Hit = 100 * 6134 / (6134 + 2000*3.4) * 2 * 85 / (85 + 85) = 47% (compared to 75% in our initial example with no merc)

This essential means that the monster will hit you 1 out of 2 swings rather than 3 out of 4 swings. Chances improved by about 33% (33% of 75 is 25, and 75 - 47 = ~25)

Now to compare with the example at lvl 90 and double defense:

Chance to be Hit = 100 * 6134 / (6134 + 2000*4.4) * 2 * 85 / (85 + 90) = 40% (compared to 59% with no merc)

Chances improved by almost 33% (33% of 59 =~20, and 59 - 40 = ~20)

Order of Operations

Defense is the first that rolls

When using shield or claws or amazon Dodge/Evade/Avoid, defense is the first that rolls. This means that shield block is rolled only if defense failed to block the attack. If the shield fails to block it, then Dodge/Evade/Avoid Rolls. (Note: this is not a fact, it's speculation based on actual game testing)

This is very important, for example, for Spearazons that use Fend, since the only way to minimize the D/A/E bug (if you put points in there) is to have very high defense.

If for example, we use a shield and have 75% chance to block in our first calculation, then the chance that a physical attack (that uses Attack rating) will hit us becomes:

  • Chance to receive the attack = 75% * (1 - .75) = 19% (rounded)

Obviously the shield drastically improves our chances to avoid the attack, but let's not forget blocking takes time (frames), and not all classes use a shield all the time. Mercenaries do not use shields. Those in act 3 do not use the shield for blocking!

If we play a javazon that has 50% D/A/E then the 19% above becomes 9% (rounded):

So if you take your javazon in a fight with a group of Death Lords in Hell, and you have about 2000 defense, 75 shield CTB, and 50% Dodge, you will rarely be hit, but you will hear the shield blocking quite a lot! (This will interrupt your lighning fury or Plague javelin for example)

Defense and blocking

When defense "blocks" an attack it has no animation and it will not interrupt your attack (or casting). This is different from the Shield block animation or the amazon D/A/E (which will interrupt your attacks even if you don't get the animation)

How defense "reduces" the damage:

While no matter your amount of defense, you will always receive the same damage per hit, the advantage is that you get hit less often.

So if you are fighting a group of frenzied Death Lords (95 damage average), and they swing about 10 hits per second (given enough lords there), you will get about 950 damage a second with low defense and no shield! Now if you look at our example, where 25% of the attacks don't get to you due to 2000 defense, the damage in a second becomes 712, and if you have a merc with defiance, it becomes 446 per second compared to 950 per second! (similar effect to amplify damage curse) This might give you enough time to leech back or heal with a pot.

This is the only way that defense "reduces" damage!

When is defense important and why

Defense is equally important in pretty much all areas. There are places where most monsters are casters, so defense doesn't help that much, but very few places have much more casters than physical attackers.

Regarding character builds

Different character builds benefit differently from their defense. This is an important aspect of the guide, and I will go over some common builds and say how much they benefit from defense. I will list them from the most benefiting builds to the least benefiting ones.

Most benefiting: Melee builds without shields benefit the most from defense!

Examples: Frenzy barbarians, Spearazons, any 2-handed weapon build, Barbs, melee mercs!

Frenzy barbarians spend more time facing a group of monsters and attacking them. A high amount of defense can make them immortal with some life leech! They can walk by default, and use the frenzy speed boost to close on enemies. Spearazons need lots of defense if they plan to use Fend, since D/A/E will get them killed! Two-handed weapon builds (such as IK barbs) do not have shields, so defense will help them.

Melee mercs will make good use of defense, put Ethereal bugged armors on them!

You don't necessarily need to make Stone, but any Ethereal armor socketed with the Cube recipie (Tal + Thul + pTopaz = "the triple T" (C) Alecz) will have significantly better defense making their healing rate more effective. Barbs have skills that can greatly improve their defense (Shout, Stone skin, Defiance, Holy Shield). For these builds 100 extra defense can easily become 500 extra defense!

Some benefits: Paladins and Builds that plan to use defiance mercs and are not included in the above group

  • Examples: Paladins, Bowazons, Sorcs.

If you plan to use a defiance merc you might as well consider defense rating. The mercs will give you good bonuses to your defense. Bowazons that use Strafe can really use high defense, especially since they might not put in D/A/E which will interrupt strafe (not visually, but all arrows will miss). Paladins that use shields and Holy shield can achieve very high defense ratings. Sorcs also have cold armors which with +skills can give a considerable boost.

Less benefiting: Javazons, necromancers (other than melee maybe), builds with shields that are not paladins or barbs and plan to use other mercs than defiance mercs (e.g prayer/insight sorcs).

These builds will have trouble boosting their base defense. They usually have lower strength, and need more resists, so their armor boosts are not significant.

Javazons and necro's would more likely use shields with high block and D/A/E (jab is interruptible afaik), or Bone Armor for more protection.


Essentially if you have ways of getting high defense, than you should aim for it. If you are a LF java zon, then defense is pretty useless, you don't engage in melee very often, you can have max Chance to block on shield, and you have D/A/E ----> forget about defense!

If you are a Frenzy barbarian, that puts 1 point in Stone Skin, and several in shout (even if only for the BO synergy), then look for high defense items, grab a defiance merc and have frenzied Death Lords for dinner!

Regarding situations

Conviction! Level 12 Conviction reduces the defense by 83%. So if we take our first example with 2000 defense, then the actual defense becomes 340. Plugging this number in the equation to see the chances to get hit we obtain:

Chance to be Hit = 100 * 6134 / (6134 + 2000 - 2000*0.83) * 2 * 85 / (85 + 85) = 95% (94.7%)

This should come to no surprise! We all know how our mercs evaporate when they have conviction on them (except defiance mercs - talk about that soon), due to the huge amounts of successful hits landed on them. I don't know if it is probable, but imagine fighting a group of Death Lords when you have conviction on you...

Now lets see the effect of defense boosting skills (Shout, Defiance, Stone skin, Cold armors, Holy Shields, Bear form), and Conviction.

Taking our example (-83% def from conviction, +100% defense from bonus), the chance to hit become:

Chance to be Hit = 100 * 6134 / [6134 + 2000*(1+ 1 - 0.83)]* 2 * 85 / (85 + 85) = 72% (so we are almost back to normal)

The point is that conviction will reduce your defense by a percentage of your base defense (all items added together). Any bonus to your defense that is at least 100% is guaranteed to eliminate the effect of any level Conviction! So if you are a barb, and are affected by Conviction, even lvl 1 Shout is guranteed to eliminate the effect! For this reason, defiance mercs (and to some extent act3 cold mercs) will survive much better under the effect of conviction. [note that the -% resist from Conviction is not eliminated by defense]

A real game example I noticed: Prayer merc with about 3k defense ends with about 350 defense, while a defiance merc with about 9k defense (due to defiance) ends up with about 6.5k defense. This is how the effec of conviction is negated.

Guide Conclusions

  1. if you can get high defense, aim for it
  2. defense can "reduce" (over time) damage that requires attack rating
  3. defense is useless against spells, elemental, posison, and magical attacks
  4. If you have high defense, walk, don't run! (when around enemies)
  5. Defense is only useful in high amounts!