I mean, if I have an armor that has 25 armor points, will it reduce damage more than a 20 armor points armor?

Talking about 1.10 and up

The damage formula is damage = damage * ( 1 - min( 20, max( defensePoints / 5, defensePoints - damage / ( 2 + toughness / 4 ) ) ) / 25 ).

You can figure it out. Toughness is 0 for all types of (vanilla) armor except diamond (which has 2). Defense points is the number of armor displayed in the UI.

I've asked because I've heard somewhere that going over 20 (or 30) would lead to no effects / problems

Well, yes, there is a maximum amount of damage reduction. That's what min(...) does.

12 minutes ago, Insane96MCP said:

I've asked because I've heard somewhere that going over 20 (or 30) would lead to no effects / problems

What exactly do you mean? As Draco showed, if you have damage reduction over 20, the formula will act the same as if it were 20. So it won't cause any "problem" but it also won't do anything special. Do you actually want it to do extra damage reduction, or are you just worried that an error might occur? Why are you asking this question in the first place?

3 minutes ago, jabelar said:

What exactly do you mean? As Draco showed, if you have damage reduction over 20, the formula will act the same as if it were 20.

Well, the other half is a complex formula (the part inside max(...)) that means that the more damage you take at once, the less each point of armor counts. But yes. The maximum damage reduction you can get is 80%

 

Also, hit points are a float, meaning you can (and will) take 0.01 damage in certain circumstances (death by a thousand tiny cuts).

Edited November 12, 20178 yr by Draco18s

I've just tried having an armor with 25 armor points and 3 thoughness, seems like I take no damage from damage sources that armor reduces.

Edited November 13, 20177 yr by Insane96MCP

Ok, now I know there's something wrong in Minecraft / Forge calculations.

Every one of this was tested with 25 armor points + 3 thoughness, Hard Difficulty and always standing in the same spot of the Creeper and full health

In 1.10 the creeper dealt no Damage

In 1.11 the creeper on shots me

In 1.12 I stay alive with ~3 hearts

Wth is going on?

4 hours ago, Insane96MCP said:

Ok, now I know there's something wrong in Minecraft / Forge calculations.

Every one of this was tested with 25 armor points + 3 thoughness, Hard Difficulty and always standing in the same spot of the Creeper and full health

In 1.10 the creeper dealt no Damage

In 1.11 the creeper on shots me

In 1.12 I stay alive with ~3 hearts

Wth is going on?

Probably alterations in the formula. I don't know when things were changed (and I don't go looking into them often myself), but I do know that at one point armor was a flat 4% reduction per point (which lines up with your 1.10 result). It's also possible that Forge mucked with things (I've heard comments about it, but again, never tried to verify them).

On 13/11/2017 at 5:33 PM, Draco18s said:

Probably alterations in the formula. I don't know when things were changed (and I don't go looking into them often myself), but I do know that at one point armor was a flat 4% reduction per point (which lines up with your 1.10 result). It's also possible that Forge mucked with things (I've heard comments about it, but again, never tried to verify them).

Oh yep, that https://github.com/MinecraftForge/MinecraftForge/issues/3629 has been fixed in 1.11 only

It's still strange that 1.11 and 1.12 differ

 

EDIT:
I can now confirm that in 1.10 going over 24 armor points will make you invincible since there's 4% flat damage reduction for every armor point and at 25 armor points you'll have 25*4% = 100% damage reduction.

Edited December 12, 20177 yr by Insane96MCP
Added more infos

In minecraft 1.12.2 ( and i'm pretty sure above ) i can COMFIRM. That 30 armor is actually the cap, and for armor toughness, it is 12. By the way, i just tried it and, taking 40 damage with 30 armor and 12 toughness, deals 8 damage.