This superb interactive graphic will give you a chance to discover the size of things, from the smallest to the largest. It is simple but quite wonderful. The quickest way to explain what it does is ask you to try it.
Just use the scroll button on your mouse to move between levels of magnification. (It runs in Shockwave so it will not work with iPads, iPhones and so on.)
I highly recommend you open the full-screen version, which can be found here.