How strong is Godzilla? He’s tens of thousands of tons of archosaurian might capable of devastating a megalopolis in a single night. Surely there isn’t a another character in fiction capable of surpassing, let alone matching the raw strength of Earth’s most recognizable radiationspewing reptile…
… or is there?
As you’re probably already aware, discussions like the one about to follow are not uncommon. It seems as though people have an innate desire to stack the abilities of wellknown personalities from different works against one another, but the real question is whether or not it can be done mathematically. The estimated magnitude of energy required for the strongest incarnation of a fictional character to perform their greatest feat is one possible method. Let’s give it a try!
For the sake of ease, we won’t take into consideration a character’s ability to travel near, at, or greater than the speed of light, since it inevitably causes our estimates to approach, reach, or even exceed infinity! It’s much easier to handwave these speed achievements by declaring them the result of yet unknown solutions to general relativity. That being said, let’s start with our own home team mascot, Godzilla!
Why doesn’t he do this more often?

Possessing incredible strength and a thermonuclear heat ray, Godzilla’s noteworthy feats are the stuff of legend, and there are a select few that stand out from the rest.
First, there’s GMK Godzilla’s “MiniNuke” ray. Using the delay between the flash and the bang, one can calculate that the schoolgoers who witness the mushroom cloud are only about 440 meters away from ground zero. Based on similarities to the lowyield Davy Crockett nuclear device^{ [1]}, the energy released by GMK Goji’s ray might be somewhere in the range of 42 GJ (4.2 x 10^{10} joules).
For those of you who have yet to see Godzilla vs. Hedorah (1971), please be warned. The contents of this paragraph contain spoilers. In this film, Showa Godzilla’s unique method of flight may be an entire three orders of magnitude greater than GMK Goji’s “MiniNuke” ray! The calculations took a while for this one and required not only careful observation of Godzilla’s flight footage, but also an assortment of physics formulae. Admittedly, the accuracy of these findings might be off, so if you think you have a better estimate, please feel free to send me an email (my address is located on the Site Staff page). With that disclaimer out of the way, one possible result that seems to fit the data available is 40 TJ (4.0 x 10^{13} joules) for the full 33 second flight ^{[2][3][4][5][6]}.
Would Wilhelm II approve?

Finally, there’s GFW Godzilla’s Hyper Spiral Ray. Based on the curvature of the planet at the altitude to which Keizer Ghidorah is propelled, one possible estimate of the energy behind this attack is a whopping 315 TJ (3.15 x 10^{14} joules) ^{[2]}!
Before we continue on to the competition, there are a few theoretical selfdestruct scenarios worth exploring, as well. Taking into account Godzilla vs. Destoroyah (1995) dialogue that implies an exploding Godzilla would be at least equal to the world’s combined nuclear arsenal, a conservative estimate of his explosive potential could hover around 21 EJ (2.1 x 10^{19} joules)^{ [7]}. Later on, the dialogue touches upon the possibility of a Godzilla meltdown, resulting in China Syndrome. Assuming the China Syndrome phenomenon is real in the Godzilla universe and that the reaction would terminate at the Earth’s core, we’re looking at a rough minimum of 393 YJ (3.93 x 10^{26} joules)^{ [8]}.
So, are there any fictional characters who can boast energies of an even greater magnitude? Let’s find out.
Godzilla vs. Other Fiction Heavy Weights
The joys of gastrointestinal regularity. 
The Hulk:Who knew gamma rays could unlock such an exceedingly deep well of strength? Although the Hulk has no known upper limit as of 2013 ^{[9]}, we can still try to measure his greatest feat thus far. In Marvel Comics Presents #52, the Hulk destroys an “asteroid” approximately twice the size of Earth with a single punch^{ [10]}. Assuming a similar density to planet Earth and also assuming that “twice the size” means “twice the radius”, 1.8 billion YJ (1.8 x 10^{33} joules) seems to be the minimum amount of energy required ^{[8]}. 

Goku: Despite possessing the ability to destroy planets, Goku has never actually directly taken one down. This makes an energy calculation a bit more difficult; nevertheless, we can get a little creative here by using Muten Roshi as a guide. The weakest character to wipe out a significant celestial body in the Dragon Ball universe, Roshi’s “power level” probably didn’t exceed 139 when he destroyed the (first) moon. Because the Kamehameha Wave uses latent ki energy, we can deduce that 139 is the minimum known “power level” required to blow up Earth’s natural satellite. Since 2.77 million YJ (2.77 x 10^{30} joules) of energy is enough to eliminate the moon ^{[8]}and since Goku’s highest confirmed “power level” is 150,000,000 according to Daizenshuu 7 ^{[11]}, we can conclude with a fair amount of confidence that Goku is capable of unleashing at least 2.99 trillion YJ (2.99 x 10^{36} joules) of energy. This figure would only be valid as of the Frieza Saga, so it likely increased by leaps and bounds in subsequent story arcs. 

Perhaps the “S” should stand for “Sneezing”. 
Superman:
Achoo! In Action Comics #273, it is heavily implied that Superman destroys an uninhabited stellar system… by sneezing. Assuming similar composition to our own solar system, we can roughly calculate that Superman is capable of unleashing 212 sextillion YJ (2.12 x 10^{47} joules) of energy in one astronomical expulsion of mucous ^{[12]}! It’s comforting to know that he’s conscientious enough to take it to an uninhabited realm of space, isn’t it? So Godzilla isn’t necessarily the strongest; so what? Big deal! Am I right? That doesn’t make a 50 meter tall archosaur with a thermonuclear heat ray any less awesome, does it? Didn’t think so. 

Sources: ^{[1]} Declassified US Nuclear Test Film #32 