Alright, since Dragon Cry has been accepted as Canon, we need to find out how strong Dragon Cry is, we know this scales to Animus, becasuse he absorbed the power of Dragon Cry, Fairy Heart Zeref, because he has the Ravines of Time, Along with Fairy Heart, which are the strongest sources of magic in the verse, meaning they are stronger than Dragon Cry, Acnologia, cause he is the strongest character, and Natsu for defeating Animus, Zeref, and Acnologia
Now the first way, and easiest way to Calc the feat, is to take the statement that Dragon Cry is 10x stronger than Etherion which is easy, take Etherion and multipy it by 10
At least 17 Teratons, Likely 230 Teratons*10= 170 Teratons, Likely 2.3 Petatons, so At least High 6-B, likely 6-A
However, it has been said that we can't use Multipliers (even though it would be way easier), the other way we can do this is by calculating how much it would destroy in the continent
Now thanks to DodoNova, we know the size of every country in Ishgar
DodoNova's calc: https://vsbattles.wikia.com/wiki/User_blog:DodoNova2/Etherion_Destroy_Countries_-_Fairy_Tail
Now for the Low-End, I will only use Fiore and Ilia, because those were the only two countries shown to be affected by Dragon Cry
For the Mid-End, I will use Fiore, Bosco, and Ilia, because it makes sense that everything caught inbetween Fiore and Ilia, would also be caught in the explosion
For the High-End, I will use all of Ishgar, because It was stated that Dragon Cry could maybe destroy all of Ishgar, which is the highest highball ever, and really shouldn't be used
Formula: R = Y^(1/3)*0.28
Low-End:
Fiore = 83 Px = 4327 Km
Ilia = 35 Px = 1824 Km
Fiore+Ilia = 118 Px = 6151 Km
((6151/0.28)^3) / 2
Y = 5.3006984E+12 kilotons - Continent Level
Mid-End:
Fiore = 83 Px = 4327 Km
Ilia = 35 Px = 1824 Km
Bosco = 78 Px = 4066 Km
Fiore+Ilia+Bosco = 196 Px = 10217 Km
((10217/0.28)^3) / 2
Y = 2.4292158E+13 kilotons - Multi-Continent Level (Accepted)
High-End:
Every Single Country Together = 3184 Px = 165983 Km
((165983/0.28)^3) / 2
Y = 1.0415659E+17 kilotons - Moon Level
Yeah, under no circumstance should we ever use the High End, but it is cool, to see how strong the highball is, we should use the Mid-End or Low-End, However we could also still use the 10x Etherion scale, however the Mid-End makes the most sense since everything inbetween Fiore and Ilia would be destroyed in the blast, however, Low-End is also viable as well, point is, this only scales to 4 characters, who are the God tiers of the verse, so it makes sense, that they would be vastly superior to everyone else