Everything's at an angle, so I'll have to use T H E P O W E R O F P Y T H A G E R O U S
The building is 726 pixels in WIDENESS and 406 pixels tall.. well, at least, the triangle I am using to find the actual width of it is 406 pixels tall. Anyways, a2 + b2 = c2, thereby, 527076 + 164836 = 691912 pixels, the square root of which would make for c = 831.812478868.
The explosion's triangle is 292 pixels tall and 477 pixels wide. Using the same logic, 85264 + 227529 = 312793, which means c = 559.279000142
559.279000142 ÷ 831.812478868 is 0.67236187764
The only thing I could find as per how wide a skyscraper is was this which mentions how T H I C K the world trade center was in comparison to other skyscrapers at the time. So, I guess I'll go with a 1:15 ratio, with 15 being represented by the minimum height to be a skyscraper, 100 meters.
This would make the width of it be 6.66666666667 meters. times 0.67236187764 is 4.48241251765 meters.
Now, while I'd love to see how this plays out with the fireball calculator... it only works with explosions over 1 kiloton. And considering I have no way to really get the values otherwise, I'll just pretend Airburst is a thing that works until someone in the comments tells me how to properly git gud.
((0.00224120625/0.28)^3) is 5.12827588×10^−7 Kilotons, 0.00051282758 Tons, 2.14567062819 Megajoules, Wall level
Actually, I have a way better way to pixel scale this. Should deal with Bambu's discrepancy about how not small it looks.
Of course, Dante's a bit closer to the screen then I'd like, but anglesizing is pretty hard when you don't know the distance of something to determine size with.
The building is 835 pixels side to side. Dante is 111 Pixels. 835 divided by 111 is 7.52252252252.
Dante's like, 6 feet tall, 1.83 Meters. Times 7.52252252252 is 13.7662162162 meters, which seems like a bit more realistic of a value I guess
Now, 13.7662162162 times 0.67236187764 is 9.25587898313 meters.
((0.00462793949/0.28)^3) is 0.00000451532 Kilotons, 0.00451532403 Tons, Wall level+
Then again, it's still rather rough, but it's slightly better then before.
Edit 2: Devil May Boogaloo
Turns out, there is indeed a formula for the fireball,
Radius in meters^3*((27136*1.37895 + 8649)^(1/2)/13568 - 93/13568)^2
In our case, with the radius being 4.627939491565 meters, the equation is 4.627939491565^3*((27136*1.37895+8649)^(1/2)/13568-93/13568)^2, which is...
0.00796615094925 Tons, Small Building level