how to find (calculate)this coin is under value ??
There's no way to really know for sure if a coin is undervalued, there's no calculation that you speak of. You can look at the price history of a coin and try to understand if it's lower than previously and if so - is there a valid reason. Or you can think about where a coin is relative to its competitors and then see if it is undervalued relative to them.
In pre ICO sale we may have this doubt before investing on the concern project. We have to choose the right ICO by checking the white paper information that too will help you to learn more about the project. Hence you will be able to understand that this project will long lasting some months and going forward to make money after launched as coin.
If project does not relevant to the crypto platform. It will not survive for long term. Keep in mind before go to invest on btc.