I already created an "Accurate Kaiju Masses" thread that I will link after this introduction; however, I wanted to create a thread with a more succinct explanation, as the previous thread went through a few updates in regards to what mass values were included and how said masses were determined. This is a problem as the new forum software doesn't allow one to edit their posts after 24 hours have passed (which I frankly despise but I guess it's too late for that now), hence this thread.
The link as promised: https://pacificrim.fandom.com/f/p/3886743740744056559
There are two main issues that plague the official masses for the Pacific Rim franchise, they are far too low for the volumes of what they apply to, and the proportions between them are too small (at least for the Kaiju).
Jaegers can have their general mass approximated via a scale up from humans due to similar proportions. A human at the scale of a Jaeger would have a water displacement of somewhere around 5,000 tonnes, already greatly exceeding the official masses (averaging roughly around 2,000 tons), however, Jaegers are made of metal, which is considerably denser than water. The Jaegers are supposed to be made out of metals like iron and steel, both of which are around 8 times denser than water, putting the overall mass of of a Jaeger at around 40,000 tonnes. This doesn't account for the opposite effects of Jaegers being partially hollow and Jaegers being notably buffer than the average person (and therefore more voluminous). So as to not reach too far into the realm of speculation, we will assume these two effects roughly cancel out. Therefore our estimation for the mass of a typical Jaeger is somewhere around 40,000 tonnes. Heavier Jaegers (like Cherno Alpha for instance) may be somewhere between 50,000 and 60,000 tonnes.
Kaiju are a bit more complicated to estimate. First of all we need base volumes, and luckily some users on the Space Battles forum can provide.
Raijin has a model determined water displacement of around 44,000 tonnes:
https://forums.spacebattles.com/threads/raijin-and-shrikethorn-vs-male-and-female-mutos.638524/post-46848335
Slattern has a displacement of about 110,000 tonnes:
https://forums.spacebattles.com/threads/m-u-t-o-male-godzilla-2014-v-striker-eureka-pacific-rim.422375/page-3#post-25238635
And luckily the second user also mentioned Knifehead needing to exceed his "8,700 tonne displacement" value from the movie by at least three times, bringing his total displacement close to 30,000 tonnes, a value I cross checked myself with a few measurements and whatnot.
The last thing to consider is that the Kaiju appear to have roughly neutral buoyancy at the breach. Because water would be a little denser that deep the overall mass of a Kaiju should exceed its displacement by about 7% (I decided 5-10% was an acceptable margin of error so as to not spend forever on this).
Basically, now that we have our info, we just need to create a mathematical model that outputs mass values from a simple input. I decided the input would be the ratio of the target Kaiju's mass to Knifehead's mass. A simple exponential model works well in this case.
Slattern's official mass is exactly 2.5 times that of Knifehead, while the actual difference in volume is nearly 4 times.
The model would be y = 30,000x^1.5129415947. (Log base 2.5 of 4 = 1.5129415947, meaning raising 2.5 to the power of that mess is 4, which is of course what we want because of what I discussed earlier regarding Slattern). Unfortunately this model doesn't perfectly model the mass values closer to the middle of the graph (Raijin being our example mass there), so I needed to change it a bit.
The model I came to like best for estimating Raijin's mass was (37,500x^1.41)/1.13
Putting the division into the model let me "raise" the middle part of the graph without really affecting the weights for the Kaiju on either "end" of the model.
With our model now prepared all that was left was to use it, and these are the mass values we ended up with:
Trespasser: 34,600 t
Onibaba: 22,350 t
Knifehead: 33,200 t
Mutavore: 32,000 t
Otachi: 33,000 t
Leatherback: 36,700 t
Scunner: 42,700 t
Raiju: 47,400 t
Slattern: 121,000 t
Uprising masses:
Hakuja: 19,700 t
Strikethorn: 31,300 t
Raijin: 46,000 t
Mega-Kaiju: 150,000 t
Because of the way the apparent scale of certain Kaiju was affected by the cinematography of the scene they appeared in, some may be a bit skeptical towards the validity of the comparison between some of these mass values, with the one I expect to show up being Slattern and Mega-Kaiju, so I'll include a link to a thread where I compare these two in depth.
https://pacificrim.fandom.com/f/p/4400000000000000757
What's important to realize is that this system will never be perfect simply because the official masses that were used as the basis for this were clearly determined arbitrarily, but this is still likely the best approximation we will ever get of every Kaiju's mass without every single model available in order to determine each of their volumes.
