Here are three JPG images. All three are 72 dpi with an image width of 500 pixels.

One was saved at Quality #2, another at #8 and another at #12.

Which is which (without peeking)







One of these has a file size of 65K, another is 103K and the highest quality one is 313K, almost 5 times the size of the lowest quality one and 3 times the size of the middle quality one.