No, but you can calculate how many you do block.

If you're AoE tanking a sufficiently large number of mobs, the time limit on Redoubt becomes irrelevant, because the five charges get used up before the ten seconds expire. So the chance of having Redoubt up on any given attack is the chance that Redoubt procced on at least one of the last five blows that landed, which is 1 - (0.9)^5 = 40.9%.

So Redoubt is up roughly 40% of the time in a high-target tanking situation. Therefore your average block chance is approximately:

0.4*(block chance with redoubt) + 0.6*(block chance without redoubt)

That's ignoring the effect of Holy Shield, which will slightly increase the overall block rate.

EDIT: Just realized this is only accurate if your total avoidance with Redoubt up is 100% or greater, since it assumes any hit on you will use a Redoubt charge. The math needed to calculate Redoubt's uptime if this is not the case would be substantially more complicated (I think).

Yes. I think that has been covered in this thread already, but in any case what you state is correct. Because Redoubt is a proc, you can't count on it for uncrushability. Therefore, it only really comes into play in AOE tanking situations. Rarely, if ever, does a boss have enough hits in 10 seconds to remove all your Holy Shield charges.

Please do not take that as advocation of not taking redoubt though, if only because shield spec is so good. Block values may not seem to be that impressive, but they're making significant changes in incoming mitigation. 500 off a 10k hit doesn't seem that great, but that's equivilant to putting on Shadow Embrace from a warlock. In addition, there actually aren't a lot of bosses that hit individually at the 10k level (supremius, Gruul are the only ones who come to mind), and obviously the smaller they hit the more valuable block value is going to be. 30% is highly significant.

Typically, the difference between non shield spec and shield spec is not 500, it's about 150 at higher levels. And that's not a huge number. At lower levels BV is going to be even less and it is going to be less valuable overall.

Shield spec is worth it for various reasons, but lets not exaggerate how good it is.

That might be, but I thought we were talking about the merits of shield spec.

I appologise for being unclear. At my gear point (some T5, some T4, hyjal honored ring) Shield Spec is about 120 block value for me, and I have no illusions that it will realistically scale up to 500 for 3 points. I was merely attempting to emphasize how strong shield block is in general, and failed to draw from that that the points in shield spec are quite good because it is a very well scaling benefit to a stat that a lot of newer tanks tend to overlook.

Honestly, I really wish they would untie Redoubt from SS, because while it is helpful tanking on Hyjal trash waves I find the mobs don't hit all that hard unless the abombs get the stun, at which point it's useless. On the flip side, because they do stun quite often Redoubt is up considerably more than the 40% figure above (if you ignore the stunned time) and because of the HS procs....but honestly if I go in with over 500 block value the ghouls alone run me oom in no time flat because of the weak hits they toss my way. I'm not really sure blocking more of nonspikey easy to heal damage is a good thing. Imp Devo's ~450 more AC is somewhat appealing, though I freely admit I'm an AC/stam whore.

Then again, with all the issues with prot speccing a paladin in the first place, this has got to be pretty damn far down on the list.

Edit:
For clarity's sake, lemme specify that I was referring to the bloated tree design, not the concepts.

Yeah, I was all psyched up to go in and try out my epic'd out block/block-value set on the Hyjal trash, but after getting gibbed by Abom's a few times I realized it was better to just stick with the standard max-armor/hp set. Kinda disappointing.

I forgot my Free Action Potions tonight and almost got splattered on Rage trash. Being the catch-all tank isn't so hot when your two abomination tanks are on the same connection.

edit for actual content/ideas: [Stratholme Holy Water] - scales with spelldamage (~1100 hits with 900 spelldamage, so probably ~800 hits with 400 damage), is aoe, and does holy damage. Am I wrong or is that essentially 1.5k free threat on every (undead) mob within 10 yards?

Eh, I just live through it with my post-2.3 ridiculous health pool. Haven't had a problem dying on those packs since I stopped wearing the block suit.

Oh, interesting. Instant cast too, apparently?

On a similar note, I have a bunch of [Blessed Wizard Oil] saved up from the scourge invasion a couple years ago. Shame they never re-ran that event.

Ya I find the abominations to be more of a pain than a real concern. I pop the free action potions just to help my healers out. That and hammer of justice every time it's on cooldown.

I'll have to try the holy water out. If it works well, it could conceivably help the whole raid (healers could throw a mana-free AoE attack...). If it does work, means I'll have to start running Strat and Scholo( [Dark Rune] ) on a regular basis too.

A lot of paladin tanks use the Gnomeragan as part of their BV set. It's not a use all the time trinket, but it's definitely quite good for a fair chunk of encounters out there.