That’s the size of the object in practice.
Water displacement is based on the volume of an object being introduced into the water by whatever amount it’s submerged.
You can probably calculate this on the fly by using the object bounding box as a source to calculate its volume.
Obviously, it’s not going to be 100% accurate to reality. Just assume the whole object is always completely submerged.
And that when it floats, it’s 50% of the object that’s submerged.
That is by no means accurate, but it should allow you to create interesting effects once the physics push start happening.
If you want to learn off of others work, the community ocean project has a decent breakdown of this.
It’s community made, so it isn’t necessarily the best way to do it, but it does do it…