I don't know what you mean by side view. Do you mean like front side and back side (head side and tail side), or do you mean like an "edge-on" view, so that it looks like a rod or stick? Either way, you need to get a binary image of the object and then use regionprops to get the length or diameter of it. Post an image so we can see it. regionprops gives the answer in pixels. If you need real world units, like Jan brought up, then see my attached spatial calibration demo, below in blue text.