[Raghnall]

How large is the Inquisition? Across the Imperium, I suppose there are around 100,000 Inquisitors, but is there anything to indicate roughly how many will be active in a sector? How many will there be in a given Ordo, including Ordos Minoris? What about networks and support staff; how many people will the average Inquisitor employ in their operation?

[MarcoSkoll]

Do you want the sensible answer or the "GW didn't really think it through when they did the 6thE Inquisition codex" answer?

When the 'Clave last had this discussion (which I can't find, so it may even have been on the last version of the forum) the reckoning was that on average there was less than one Inquisitor per world, but more than one for every ten. (Between 100,000 and 1,000,000 Inquisitors, basically).
Fewer than that and it starts to get really contrived when they keep running into each other. More than that and you start wondering how they ever manage to get along.

We reckoned that about half of those would be "field" Inquisitors (taking direct action in person) and the other half would be "desk" or "political" Inquisitors (working through others) - with perhaps a few retired Inquisitors, as much as an Inquisitor ever can be/would be retired.

Per sector? I'd say sectors tend to be closer to a hundred worlds than ten (you'll see a lot of Fermi estimation here). Ergo, there's probably between ten and a hundred Inquisitors in an average sector.

Per Ordo, the largest Ordo is Hereticus, and I'd guess is probably about 40-50% of the total.
Xenos is probably some 20-30% of Inquisitors.
Malleus is the smallest of the Ordo Majoris (given that even amongst the Inquisition knowing too much about daemons and the warp is a mite taboo), probably 10-15%.
Of the Ordo Minoris, most are probably in the region of a percent or two of the total.

As far as support networks? Probably thousands (even ignoring things like the crew of any ships they own). Most Inquisitors will have multiple "high ranking" agent cells, then lower ranking cells, reserve agents, agents who don't even know they're working for the Inquisition, informers, information brokers, overseers (to co-ordinate it all) and more.

The "GW didn't think it through in the 6thE codex" answer is contradicting old background (some total BS about the Ordo Hereticus having existed as a secret, even within the Inquisition) and tiny Ordos Minoris everywhere - to the point that there's massive overlap (Such as an Ordo specifically for overseeing the Ecclesiarchy, which happily falls within the Hereticus' remit) and groups of fewer than ten Inquisitors (or in one case, a single Inquisitor) being called Ordos, entirely missing that half the point of an Ordo is to be a pool of resources and allies. (This is serious. I'll call my Ordo for help. Come here me!)

[Raghnall]

When the 'Clave last had this discussion (which I can't find, so it may even have been on the last version of the forum) the reckoning was that on average there was less than one Inquisitor per world, but more than one for every ten. (Between 100,000 and 1,000,000 Inquisitors, basically).
Fewer than that and it starts to get really contrived when they keep running into each other. More than that and you start wondering how they ever manage to get along.

I've looked back in the archives and didn't find anything on this topic, so it was probably on the old 'Clave. Those figures look about right, although I would note that there are certain events that are likely to attract several Inquisitors, and particularly when more senior types take to the field, I suspect there would likely be a notable Inquisitorial presence.

I'd say sectors tend to be closer to a hundred worlds than ten (you'll see a lot of Fermi estimation here). Ergo, there's probably between ten and a hundred Inquisitors in an average sector.

The Calixis sector is just over that, so 100 seems a nice average.

The "GW didn't think it through in the 6thE codex" answer is contradicting old background (some total BS about the Ordo Hereticus having existed as a secret, even within the Inquisition) and tiny Ordos Minoris everywhere - to the point that there's massive overlap (Such as an Ordo specifically for overseeing the Ecclesiarchy, which happily falls within the Hereticus' remit) and groups of fewer than ten Inquisitors (or in one case, a single Inquisitor) being called Ordos, entirely missing that half the point of an Ordo is to be a pool of resources and allies. (This is serious. I'll call my Ordo for help. Come here me!)

Games Workshop really ought to leave the Inquisition alone. However, the Ordo Desolatus is almost certainly cover for something big, so I would like that to be explored. Surely Games Workshop can't have been stupid enough to actually create a real Ordo with only one member. Right?

[MarcoSkoll]

Games Workshop really ought to leave the Inquisition alone.

My option for justifying most of the Ordos they introduced would be for them to be sub-factions of larger Ordos. That's fair enough - within the Ordo Hereticus, there will certainly be those who specialise further (watching the Ecclesiarchy, Imperial Guard, etc) - but the Enemy Within, Enemy Without and Enemy Beyond remits are broad enough that there's not a lot of space between them.

The older fluff about Ordos Minoris like the Sicarius or Sepultrum, while a little questionable, makes more sense. While Imperial assassins and warp-plagues would cross over to an extent (with the Hereticus and Malleus respectively), you can see why they might exist separately - they do call for pretty specialist skills and equipment.

Something like the Imperial Guard though does not strike me as a particularly unique threat. While a rogue regiment might possess more martial power than a typical heretic cult, that's not really a problem that's solved by breaking off into a smaller and less powerful Ordo!

Some of the new Ordos do make a bit of sense - for certain values of new, of course; I'd cooked up the concept of my Ordo Perditus (specialising in secrets and records) some time before they'd come out with things like the Scriptus or Redactus.

And then, yes, there is potentially some interesting speculation to be had about some of the more obscure Ordos. Although I have to say:
-  that Ordos where no-one knows what they do again defeats some of their point. ("This sounds like a job for the Ordo Necros!" "What do they do?" "Hell if I know.")
- And in the same way as with the two unknown legions, I suspect it's one of those things where any actual answer would be less interesting than not knowing.