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Overview of Armor and Damage Reduction

20.10.18 | RehcraM 2977

Introduction

When getting an item from neutral creeps, it's sometimes clear as day which hero should be have it. This is, however, not always the case. In this article I'll be explaining the concept of "Armor" and "Damage Reduction". Hopefully,  it will give you a better understanding to which hero you should distribute which armor-enhancing items. In other words, we'll try to figure out who's the Lord of the Rings of Protection! 

Damage Reduction

As you probably know armor reduces the amount of physical damage taken. As you may also have heard, each armor point increases your effective health points (EHP) by 6% (more on that later). But to understand why some heroes benefit more from armor than others, we have to dive into a slightly more abstract concept: damage reduction!

As written on the Battle.net website damage reduction (and damage increment for negative armor) is calculated by the following formula:

Damage Reduction = ((armor)*constant)/(1+constant*(armor)

(Damage Increment = 2-(1-constant)^(-armor))

The "constant" (also referred to as 'armor constant'), is simply a set effectiveness of armor, which is also where the earlier mentioned 6% EHP increment comes from. The armor constant can be found (and changed) in the World Editor, under Advanced>Gameplay Constants:

So, with that understood, let's take a look at what the given damage reduction equation looks like for armor points 1-1000. 

We can see that it's a rational function, from which we can conclude two very important things:

  1. You'll never be able to reach 100% damage reduction no matter how much armor you gain.
  2. The first percentile of armor is much more effective that the last percentile.

Effective Health Points

I promised I'd return to touch on EHP and the correlation between it and damage reduction. Normally we'd also regard other variables than armor, like Evasion and magic resistance, but to keep it as simple as possible, this example's only variable is armor (and base HP, of course).

By using the previous formula for damage reduction, we can set up an equation for EHP without too much hassle. We set the base health pool to 1000. If my previous proposition about every armor point increasing the total health pool by 6% is correct, setting the armor to 1 would get us 1060 HP.

From this function we can also conclude two things:

  1. EHP scales linearly with armor points.
  2. It is correct that the increment is 6% pr. armor point.

So even though we, in theory, can get an infinite big EHP, we will never be indestructible as we cannot reach 100% damage reduction.

Below is an overview of more realistic amounts of armor and their respective damage reduction/EHP 

Source: Liquipedia

Conclusion 

To get us back on track on the article's topic, let's answer the initial question: Who should carry armor enhancing items? Who should be the Lord of the Rings?

Well, as we now know, armor increases EHP percentage-wise from the hero's health pool and armor is less effective regarding damage reduction. Therefore the most effective use of extra armor is on beefy units with little armor such as the Goblin Alchemist, the Crypt Lord, and the Tauren Chieftain (as my cover slightly hinted at). 

I hope you enjoyed this article and learned something new!

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