Rodent Wars Forum

There are several ways to calculate explosion energy. A great example of this is the Turbolaser yield calculations thread, where both methods are used.


Radius:
Figure out the radius (distance from edge to center) of the explosion. Then, use one of these calculators to find out the yield:
Conventional Explosives Effects Calculator (Dutch's favorite radius calculator)
Nuclear Weapon Effects Calculator (for very large blasts only)
NUKEMAP (for estimating the overall effect)

This method tends to underestimate yields for smaller explosions (below about 100g), and so is very subjective due to how much it is based on the calculator's conjecture. See here for a less subjective way to estimate by radius.


Destruction:
To find out the energy this way, just figure out how much destruction the blast caused. If it vaporized 100 grams of iron, you can calculate it from that, as iron requires 7.63 MJ/kg to vaporize. Just multiply the amount of iron melted (in kilograms) by 7.63, getting an answer of, in this case, 0.763MJ. Then you can convert it into TNT, using this calculator (convert your answer to joules first):
Joules to kilograms-of-TNT
     This method is pretty exact by our standards, but remember that specific heat changes with temperature (the figures we use are averages), so it will never be experiment-level.

Or, if the blast violently fragmented 250 cubic centimeters of granite, then according to a VS Battles Wiki user we should multiply 250 by the violent fragmentation energy of granite (175 J/cc). This gives us 43750 joules, or 43.750 kilojoules.
     The destruction-energy method is only a guesstimate. Though it admittedly does not reflect the complex nature of material interactions in real life, comparing it to other methods shows that it is precise enough for the purpose of rough approximation.


KE:
Say an explosion hurls 100g of material away. We know that the yield of said explosion must be at least equal to the kinetic energy of the material. So if the material is thrown at about 100 m/s, then the KE is roughly 500,000 joules. Now, this is of course an underestimation since it is the minimum, only sufficient to hurl away the material with no other effects (melting, fireballs, other shockwave effects, vaporization, radiation). For instance, this method is used along with the melting method here.


Resources:
VS Battles Wiki: Explosion Yield Calculations
VS Battles Wiki: Table of Destruction Values
Some missing destruction values
StarDestroyer.net: Asteroid Destruction Calculator
StarDestroyer.net: Nuclear Weapon Effects Calculator
Conventional Explosives Effects Calculator
NUKEMAP