So Fireball makes a 20ft radius sphere. That’s a sphere with a volume of 33,510.322 ft^3 A sphere 100 times bigger would be 3,351,032.2 ft^3 Such a sphere would have a radius of 92.832ft The range of fireball is 150ft, so you could safely cast it’s 100x magnitude counterpart. Of course this is a very simplified idea of what 100x magnitude fireball could do. For instance, does it do 100x the fire damage? ~2,800? That’s over 50.9x more than lava (which is ~55). Does that mean it’s 50.9x hotter than lava? Making it 35,630-61,080 C, 6-11x hotter than the surface of the sun? These calculations are all fast and loose as actual explosion calculations are too complicated for my little brain.