Difference between RAW file size and Photoshop Image size

I have a RAW file from a 24 megapixel camera. The RAW file is about 25MB in size, looking at it in OS X. When I load the RAW into Photoshop and then look at Image > Image Size in CC 2014, Photoshop reports a size of 58MB. I find this dialog useful as it allows me to assess how big I can print at various DPI but I wonder about why the file size has now doubled?

I am guessing that this is because Photoshop has to hold the data in an RGB color space vs the native bayer sensor format of the camera.

Interestingly, when I save the file as a PSD, file size grows to 110MB. I am considering a higher megapixel camera but I shudder to think what the end file sizes will be.