MINI LESSON: CUPS (2 of 8)
When I draw/paint cups, I am always shooting for pretty accurate proportions, so that the cup makes sense in the scene. If it's a little fatter or taller than in real life, that's ok, no one will complain, but if the proportions of the ellipse don't jive with the height of the cup, it will look "weird," and that will make viewers uncomfortable.
So, I measure, and here's how. I hold my paintbrush straight out from my body, with my elbow locked, brush parallel with my face, and my thumb near the end. First I measure the height of the ellipse, as shown in the picture, with the tip of the brush at the top, and my thumbnail at the ellipse bottom.
You can use this tool to measure other parts of the cup too, like over-all width to over-all height or ellipse width to ellipse height. You can also use it to measure, well, just about anything that you're drawing/painting. It can be especially helpful when you've got objects receding in space. You know they should get smaller as they recede, but your brain is going to try and keep you from drawing it that way. Believe me. So measure and prove it to your brain.