How to counter Kha'Zix
Let us take a look on how to beat Kha'Zix. We will look at champions who are strong against Kha'Zix and who are weak against Kha'Zix. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Jungle champion who counters Kha'Zix. You can already win in champion select with the right counters for Kha'Zix. If you want to know how to counter Kha'Zix then you need to take into account the best picks vs Kha'Zix and the worst picks vs Kha'Zix. This Kha'Zix counter data is based on matches played by Pros on patch 14.9 and previous ones. It is important to see whether Pros counter picked Kha'Zix or whether they played as Kha'Zix.
Champions used by Pros to counter pick Kha'Zix
Looking at the matches from Pros (see table Pros counter picked Kha'Zix) we can see that they picked 
Lee Sin most often to counter pick Kha'Zix. The matchup Lee Sin vs Kha'Zix occured 43 times. Kha'Zix has 24 wins and 19 losses in this matchup. Learn how to counter pick Lee Sin to get another perspective on the data.
Lane outcome for Kha'Zix
When looking at Kha'Zix counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Kha'Zix. The lane outcome of Kha'Zix consists of three outcomes: Win, Loss or Draw. Let's take a look of Kha'Zix lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Kha'Zix.
Conclusion
Analyze the available data and learn how to beat Kha'Zix. To master Kha'Zix take also a look on Kha'Zix builds and runes for Kha'Zix. Good luck, Summoner!