Here I am with another attempt to upgrade dragon waifus. Here we see Elma and Tohru creating an explosion whose height reaches well past Earth's atmosphere. I'll be using two different methods to try and calculate the yield: radius and total area of the explosion.
Here are the pages of the manga for context.
Radius
After using this little doohickey I get 658400 megatons which is 2.754746e+21 joules. According to the Explosion Yield Calc page I need to multiply it by 0.5 because reasons, then I'll need to do so again since Elma and Tohru did this together. This gives me 6.886865e+20 or 164 gigatons or Large Island level
Total Area
Now I personally really don't want to rely on the radius only, considering the impressiveness of this explosion is in how high it reached.
So 1319 km, plus another 100 km to reach from Earth's surface to the outermost edge of its atmosphere.
1419*439 = 622941 km^2 for the area of this explosion. But guess what? This page caps out at 86614.1 km, so I have no idea what the resulting destructive value even is! All I know is it's waaaay higher than Multi-Continent level or High 6-A
So if someone could please tell me how to figure out the exact value, that would be absolutely wonderful.
ArbitraryNumbers's Version
The radius is 219.5 km and the height is 1,319 km. So that means the volume is 2e+8 km^3 (2e+23 cm^3) if we use the volume of a cylinder.
Let's use the density of 1.003 kg/m^3 (1.003e-6 kg/cm^3)
1.003e-6 * 2e+23 = 2.006e+17 kg
Let's assume 10 seconds for a higher end, 15 seconds for a lower end.
1,319 km / 15 seconds = 87,933.3333 m/s
0.5(2.006e+17) * 87,933.3333^2 = 7.7554679e+26 joules, or 185 Petatons of TNT - Multi-Continent level
1,319 km / 10 seconds = 131,900 m/s
0.5(2.006e+17) * 131,900^2 = 1.7449803e+27 joules, or 417 Petatons of TNT - Multi-Continent level