Understanding Photoshops Image Size

I've long wondered why Photoshop displays a much larger size of an image than it really is. For example, I opened this barn photo which is in a .jpg format and is just over 2 MB in size.
However, Photoshop is telling me that the photograph is just over 6 MB under the Image Size. I didn't understand why Photoshop displays a much larger size for the image than it actually is.
I learned that Photoshop is showing me how large the image would be if I saved it again in an uncompressed native .psd file. Photoshop adds a lot of additional information/overhead in its native format that I wouldn't need when saving it as a .jpg file.
Now, finally this is making a little more sense when I see such a variation in file size! I hope this helps you too.