Effective Health

Effective Health (EHP) is the amount of health that the player effectively has when considering both and  in union. EHP is a useful metric for calculating which armor is better than another armor.

The best way to increase EHP is to increase whichever stat is lower (Health or Defense); however, there are exceptions. If one would have to choose between 50 defense or 10 health, one should probably go with the defense no matter how low your health is.

Formula
The formula for EHP is

$$HP \times (\frac{Def}{100}+1)$$

For example, if is 200 and  is 100, the formula is:

$$100 \times (\frac{200}{100}+1)$$ = $$100 \times 3$$ = 300 EHP

With 300 EHP, meaning with 100 and 200, the player can take as much damage without dying as someone who has 300  and 0  could.

True Defense and True Damage
When normal damage is applied, is just added onto the defense value. However, if facing a foe that deals, then the EHP formula should replace any reference of with , but otherwise it is calculated the same way.

List of important armor sets and their EHPs
Note: Full set bonus maxed if applicable.

If decimal amounts of health and Defense come into the equation, they are not rounded. This means some numbers are possibly inaccurate by about 0.1% or so.

The EHP formula falls apart a bit when dealing with Protector Dragon Armor because the formula assumes that the player is at full health, but Protector Dragon Armor gets more defense when at less than full health. To remedy this, inputs were added into the formula for the health of full health Protector and the defense of half health Protector in order to create an "Effective Effective Health" for it. It's still an imperfect estimate, though. The armor abilities are calculated on sets such as old armor.

Also Note: Diver's Armor with a Level 100 Legendary Flying Fish Pet might be very good, but it requires a high amount of effort in order to obtain the pet, as well as being outclassed EHP wise by other armor through the use of another pet (such as the Blue Whale).

Mastiff Armor
Note: Although Mastiff Armor seems incredible when compared with the other armor sets, note that Mastiff armor has many flaws. It makes critical damage half as effective as normal, which only becomes a bigger price to pay the more critical damage the user has. Also, the other armor sets can be drastically improved further with EHP increasing upgrades such as reforges, talismans, and Growth VI. These could potentially double or even triple EHP with other armor sets.

Effective Health per second
Effective Health per second or "EHP/s" is the EHP that a player heals per second.

The formula is the same as EHP but applying it to the Health regenerated every second.

For example, if Defense is 200 and regeneration is 100, the formula is:

$$100 \times (\frac{200}{100}+1)$$

EHP/s is mainly related to tank builds but is also important for any other class. The higher the player's EHP/s is, the longer survivability the player will have in combat.

An example of the relevance of EHP/s is two players, one with 2000 EHP and 250 EHP/s and the other with 1000 EHP and 500 EHP/s. If they both take 500 EHP in damage per second, the second person would not die as easily due to their ability to heal all the damage before taking more.

The best way to increase EHP/s is by using a Zombie Heart or any of the variants. Natural Regeneration is not ideal as it is not optimal in combat and it is only a small amount of EHP/s.

The Life Steal enchant also counts towards EHP/s and it's one of the main components of it.

Another way not listed there is summoning Zombies with a Reaper Scythe and have them dealing damage. By doing that, the player will have another big "passive" method of regeneration.