Intro[]
Prompted by this post by ByAsura, I decided to calc the storm Gilthunder made.
First of all, as the thread shows, the storm was clearly created by Gilthunder. It suddenly appeared as he did, and the lightning that came from it was created by him as well. Furthermore, Gilthunder has created clouds in the sky from which he summons lightning on other occassions, such as here:
Scaling the Storm[]
With that out of the way, let's scale the size of the cloud and determine what kind it is.
Hawk, known for his nose, says it "smells like rainclouds." This makes it a nimbostratus cloud.
We aren't given much of a picture for proper scaling, but that actually isn't a problem. For those who read the manga, you'd know that Meliodas and co. were currently deep in the middle of the Forest of White Dreams, which is where Diane was hiding out. Lore-wise, the forest is very dense and fog-covered which makes it difficult to travel through. However, the picture we are given shows a view of the entire storm, from an area without any trees. This implies the shot is shown from outside the forest, and that the storm covers the entire forest. And to back that up further, the complete shot of the Forest from far away is a sloped mountain like a dome , which perfectly matches the foggy dome seen below Gilthunder's storm.
It is clearly not just one cloud either, it's an entire storm. While the main cloud is shown and stated to be gigantic, covering the whole forest, the rest of the sky is also dark and turbulently drawn, despite it being daytime, clearly showing an entire storm.
The above picture is the most current map of Britannia from the 2nd fanbook. Pixel scaling gives us a cross-forest length of roughly 22 km.
I realize that the map is stylized and so pixel scaling is questionable at best (20 km tower lol) but the forest size is actually consistent with the average size of a real life thunderstorm, 24 km. Furthermore, with lack of a better way to scale, and the forest being canonically gigantic, as shown in the full view shot above, 22 km is an appropriate estimate.
Calc[]
The calc method here is shamelessly taken from Kepekley23's Rain Tiger at Will Calc, so props to him.
Average thickness of a nimbostratus cloud is 2000m
Volume of storm = pi*11000^2*2000 = 7.603e11 cubic meters
Mass of clouds = 7.625e11 kg
Temperature of clouds is 19.2 degrees Celcius, dewpoint is 9.6 degrees Celsius
Energy required to change the temperature: q1 = specific heat capacity*mass*temp = 1.003*7.625e11*(19.2-9.6) = 7.342e12 J
Latent heat of condensation: q2 = Mass*latent heat = (7.625e11 kg)*(2455653.15072 J/kg) = 1.872e18 J
q1 + q2 = 1.872e18 J (q1 is negligible)
About 447 megatons, Mountain level
Is it an outlier?[]
At first people will likely call this an outlier, but it might not actually be. This is long, but stay with me.
First of all, it surprisingly fits with the scaling. When Meliodas took a bunch of attacks from the 6-B Commandments to power his Revenge Counter, Gowther stated it was 30 times the energy he showed at the battle against Hendrickson. He took a 54th Combo Star hit from Derieri, a Hellfire Bird from Monspeet, a Form One: Basquias blast from Gloxinia, and a Milky Way Breaker Blade from Fraudrin. Add up four mid-6-B level attacks, divide by 30, and the energy at the capital falls in the lower end of 6-C. At the capital, there were maybe a dozen actually important attacks along with a bunch of nameless fodder knights. Dividing the total energy by the number of non-fodder and each of them would be mountain level.
That's not all, there's another mountain level feat:
The Seven Deadly Sins novel "Seven Days" is written by author Mamoru Isawa, but unlike many light novel adaptations Nakaba was heavily involved. He actually did the artwork for the novel, which expands on the seven days spent together by Elaine and Ban, the important parts already being in the main manga.
The novel clarified that the Sacred Tree is "larger than any mountain" and the manga adaptation, also written by Mamoru Isawa, makes that very clear multiple times.
The Red Demon's massive hellfire explosion was calced by Spino, ThePerpetual ok'd the math but it was deemed an outlier at the time, but with this feat it doesn't seem that way as much.