Luma

So each titan is

60.0 metres tall

19.5 metres wide (at the shoulder)

10.5 metres thick (front to back)

  9.0 metres foot length

First obstacle: thickness. As seen in the manga, the walls aren’t that thick. It’s true that the diagram is of Berthold’s Colossal, rather than the walls’ colossals, though, so it’s possible the Wall Titans are thinner. Or maybe they’re soft and are compressed inside the walls lol.

The other “difficulty”, as usual, is that there are a number of variables we just have to eyeball or take as face value, namely:

The actual perimeter of the walls

For simplicity’s sake I’ll use the [physically impossible but] generally accepted notion that the walls are 3 concentric, perfect circles of 250, 380 and 480 km of radius respectively.

That means the circumference of the walls is:

Wall Sina                      1,572 km

Wall Rose                     2,388 km

Wall Maria                     3,016 km

Total circumference    6,976 km

The districts walls

To this we must add the length of the districts walls, which unlike the circumference of the wall, we don’t know and, as I’ve discussed before, the graphic evidence we have is quite poor and contradictory at best, when not simply incoherent. In our world, it would make sense if the districts were different sizes (there is a reason we always hear about the same ones, after all), but we tend to imagine them as all the same size which, if we take into account that the walls were created by ₊˚⊹ magic ₊˚⊹, isn’t without logic—In that case, Utopia residents probably enjoy larger houses at lower prices than, say, their Trost counterparts.

From the measures taken for my last essay, the curved walls of the districts that jut out from the main wall seem to be between 620 and 2,900 metres long; from all the different approximations (nine) that I was able to measure, I got an average district wall length of 1,312 metres. A bit bigger than Carcassone’s inner city. I’ll take this measure as standard size.

So 1,312 m × 12 districts = 15,744 m or 15.75 km

Putting it together

So we have a total of:

6,976 km of walls + 15.75 km of districts walls = 6,991.75 km of titans standing side by side.

I’ll round that up to 6,992 for simplicity.

6,992 km = 6,992,000 m

Each titan is 19.5 m wide

6,992,000 ÷ 19.5 = 358,564 titans.

Based on this (approximate) numbers,

There are 358,564 titans inside the walls.

A tad fewer than the “tens of millions” Willy Tybur says in Ch. 99. —This might be him [or Marley’s propaganda] blowing it up to get his way, as Eren himself speaks of “thousands” when discussing the Rumbling (sorry, lost the ch. number where he says so)

COVERAGE

Still, almost 358,600 titans are a lot of titans. How much damage can they do?

A lot, sure. Every life is precious. But in a planetary scale, the extent and seriousness of the actual destruction depend on a lot of variables, for instance:

How do they move? They advance in a tight formation, but how tight? Do they tread carefully to make sure they stomp everything evenly or do they just walk on and if they miss spots, well, good luck for those who were on that spot, I guess.

From what I can infer from the manga, the latter is true. The titans walk blindly, eyes to the front, they don’t see what they step on. We even see some tumbling and falling in some panels. They also walk close, but not grazing shoulders.

That brings up another question that doesn’t have a clear answer: what happens when they encounter an obstacle that’s too steep or tall to just step on? What if they run into, say, the 110-metres-tall White Cliffs of Dover? Do they surround it? Or do they keep bumping into them forever, like a faulty Roomba?

Fort Salta itself doesn’t look like something the advancing column could simply climb. Maybe a couple of titans could haphazardly find the road that leads to the top of the mesa, if that road was wide enough (20 m minimum) for a titan to walk on it which, by the looks of it, doesn’t seem to be the case (for reference, New York’s 5th Avenue is 16,5 m wide, not counting the sidewalks).

Either way, since we don’t ever see any titans going backwards to finish the job, there would totally be “pockets” of land left untouched by the Rumbling. (Funny that Yams didn’t think about this, seeing as his hometown itself is surrounded by mountains.)

Moreover, there is the question of how much terrain do they cover at a given time. If all 358,600 titans walked in a single row side by side, that line would extend for almost 9,000 km—But they would leave a lot of undamaged “pockets” behind, either because of the space there is between each individual foot and step, and because any fallen titan would create an even bigger space in between, or shrink the line. Imagine a bunch of gardeners each with a lawn mower advancing on a football field; there will be strips of unmowed lawn left behind in the spaces between them, unless you send in a second row of gardeners mowing those strips.

Therefore, it’s only logical, as canon shows, that the titans advance in a multiple rank (row) formation. Though “formation" might be a misnomer, as they don’t seem to be very evenly spaced, nor is it clear how many ranks there are. Here, I’ve calculated the rank length based on how many ranks there are. Please note that, for this, I’ve bumped the titan width to 25 m, as the titans walk close side by side but not so close that they touch shoulders.

Ranks  Titans/rank        Rank width in km

1            358,600                8,965

2            179,300                4,483

3            119,533                2,988

4            89,650                   2,241

5            71,720                   1,793

In the panoramic views from ch. 126 onwards, there seems to be between 3-5 ranks. However, in Odiha (ch. 132) and in the final battle, the column is much thicker. It is likely, too, from the looks of the final battle, that the ranks are higher in number close to the Founder Titan and they thin out to the sides; that would mean the damage is not even across the stampede. Whether the formation stays stable or they concentrate or spread out as they go, in any case, there would seem like the whole group never exceeds 2,900 km width. Which is still a lot, but not enough to destroy the whole continent in less than a week.