The mathematics of Shield Block vs Shield Barrier

[Deleted]

Can someone summarize briefly the general guidelines on what is best for each situation? I figure it might depend on the gear but let's assume average gear or a reference gear of your choice. If I recall correctly blocking was superior against multiple targets/multiple attacks. Is that still the general guideline?

[Valech]

Use Shieldblock against all bosses, that use physical attacks on you. Bosses, that solely resort to magic attacks are rare anyway. Current tier exception might be Dia Darkwhisper, who only uses meaningful physical attacks in her Nightmare Visage phase or if interrupted.
With improving gear, you will see, that you still have rage left/generate more rage then you can pump into shieldblock, due to shieldblock´s nature of having a maximum amount of available stacks. Whenever that occurs, bleed the rest of your rage off into shieldbarriers.
If you face an unblockable attack or damage from dots/aoe, without currently tanking anything, that physically hits you, shieldbarrier obviously is to be preferred.
Be sure to understand, that the prot warrior class trinket furthermore complicates the relation between Blocks and Barriers.

Tl;dr: Use Shieldblock whenever something hits you, use excess rage for barriers.

[Marok]

Shield Block and Shield Barrier both last 6 seconds, so it's best to think of it as "which ability will reduce the most damage over these 6 seconds?" In most cases, that would be Shield Block. There are situations where a boss could have a slow/erratic swing timer, making Barrier worth using over Block. Also, sometimes it's not optimal to think about Block/Barrier usage in terms of what will reduce the most damage over 6 seconds, but rather something like 0.5 seconds or 1 second. For example, say you're tanking Tyrant Velhari, you take a big hit and you're sitting at 25% HP. Would it be better to use Block or Barrier? Well, Block would reduce more damage over it's 6 second duration, however, you're one hit away from death, meaning you probably have under 2 seconds to live. In that case, using Barrier would be better. Math:

You have 25% of your 600,000 health pool. The boss hits for 300K (before mitigation).

So, you have 150,000 health and you're about to be hit for 300K.

You use Block:

The hit is reduced by 30%. 300 * 0.7 = 210. You're hit for 210K and you die.

You use Barrier:

You probably have high resolve, so let's say you Barrier for 175K. You live with 25K health left. At this point hopefully you're healed up and you can go back to using Block.

Just to look at how it breaks down if you were at full health:

You block 3 hits over 6 seconds (let's say the boss has a 1.75 swing timer). 300 * 0.7 * 3 = 630K total damage taken.

You barrier for 175K. 900 - 175 = 675K total damage taken over 6 seconds.

It's close, but Block wins.

This also shows how just spamming Barrier during Last Stand with 4-piece is better than using Shield Block. One 400K Barrier: 900 - 400 = 500K total damage taken.

To sum it up, use Shield Block if the boss is actively hitting you. Use Shield Barrier if the damage incoming in unblockable, if you'll die from the next hit, you're out of Shield Block charges, or if Last Stand is up (with 4-piece).

[Kirbypro]

If you have Block charges and you are tanking stuff, use Block. There are intricacies on how to use Block efficiently but unless you are doing mythic Archi or something you don't need to worry about it. At this point when we overgear everything, as long as actually you use the spell, you'll be generally fine.

If your health is spiking super low, use Barrier. Doesn't matter if you needed that rage for a Block.

If you are rage capping, use Heroic Strike. Using Barrier at high rage generally messes up your rage management unless you have Shield Slam or Revenge ready to go to get you above 60 rage. (Maybe this is wrong, I haven't tanked in a year. if your Block is on CD for a few more seconds you can dump rage on Barrier. If you have Block charges ready to use, using a Barrier might mess up your timing.)

If you have 4-set and last stand up, only Barrier. Keep spamming that cuz apparently you cannot die.

Lastly, don't overlap Barriers, get an Aura to track the Barrier amount and duration.