Body size matters the most, and as centaurs are the entire body of a horse (minus the head) plus the upper body and head
of a humanoid, a good approximate is Horse size(100000) + 1/2 Human size(70000) = Centaur size (135000). The formula which can be recycled for onocentaurs and the like.
hey, you stop at that.
horse size is nothing near 100 kilos. 400 kilograms is the lowest possible realistic estimate for anything that's going to be called a horse not a pony.
EDIT: i'm feeling a bit sorry now that i've read the whole thread and seen you have your numbers corrected. Yes, 535 kilograms is much better.
I just want to point something out here, and this is that body size
is not measured in grams. Size is instead measured in cubic centimeters. As such the current raws do not state that the centaur weighs 535 kilograms. They instead state that the centaur has a
volume of 535,000 cm^3, or about 7.5x the volume of the average adult human.
Weight, on the other hand, is determined by taking the density of the various tissues that make up the centaur's body (flesh, bone, muscles, etc.) and figuring out how much each individual body part of the centaur weighs by size*tissue density, and then adding all of those weights together.
The real problem here was that he used the child horse size (100,000) instead of the adult one (500,000). He's fixed it now to have the sizes right now to use the adult size, but don't delude yourself into thinking size=grams. It doesn't. A creature made of lead that has the same size as a creature made of adamantine will not weigh the same.