Just came across a very nicely designed website that very neatly gives a sense of how big a camera and lens combination is compared to several other cameras.
Here's an example
with the tiny new Panasonic with 24-64mm zoom versus 6 other cameras with a 24mm lens [or equivalents]. You can change camera, camera order, viewing angle and lens quite easily.
Wasn't quite sure which forum where to place this topic as lots of folk may like this tool, but this one seems the most concerned with camera size.