S5 IS replacement
[[I'm unsure of exactly how large it is.]]
Camera Size to the rescue!
Here's a comparison between the S120 and the G1X Mark II:
If you've not used the site before, you have to click on the (1) and (2) tabs on the left and change the orientation for each camera. The top-down view on both is how I made the guesstimate on the size of the S120 compared to the size of the lens on the G1X Mark II.