You could do this with a protractor. Originally I thought you'd need to do an upgrade and measure the difference, but I was making it more complicated than it needs to be.
![enter image description here](https://i.stack.imgur.com/LV8lBl.jpg)
Thankfully, the bar is exactly half a circle, this makes things a bit easier with a standard protractor. I have assumed that the bar is linear, meaning that if the bar is half full, then the Pokémon is at half of it's max CP.
The bar on this example is 110 / 180
or about 60% full.
You can then work out your estimated max level with this formula:
max = CurrentCP / (angle / 180)
Example:
max = 72 / (110 / 180)
max = 72 / 0.61
max = 118
Based on the other answer, it seems that the max CP might change as you level up, so you might need to remeasure.
But again, a physical one would have to have the same radius as the image/app on your screen.
Nope, with a ruler (or any straight edge for that matter), you can use a smaller protractor. Just put the protractor so that it's middle is in the middle of the bar and place your straight edge as indicated by the white line.
![enter image description here](https://i.stack.imgur.com/WuKn7l.jpg)
Best Answer
There are the a few articles online that come up talking about how to Evolve Wurple to either Silcoon of Cascoon. As it appears, there seems to be no way of dictating what it will evolve to at the moment:
Extracts / Passages from text
~an extract from The Sun's article
~
ExtractPassage from Player One's articleConclusion
No, it doesn't look like it, but there is no proof to show it. We are not certain, but research shows that there is probably no way to do so.