how to find (calculate)this coin is under value ??
I'm not sure what your question is. What coin are you talking about? There is only about 1300+ listed on CoinMarketCap & clearly even more in actual existence.
I find the best way to determine if a coin is under valued or not, is to check out the project of the coin as a whole. Look at the purpose of the coin, the roadmap and the white paper. Then see if the development of the coin is still active.
After you have done your legitimate research, the rest is a guess or a gut feeling. You can also check the historic charts of coins that have been around a while to try to determine a pattern. It may also be good to watch numerous coins on social media for news announcements. Coins regularly pump after big news.