STAB question...

[Trae of the Earth]

so i was asked, How much extra power does STAB give to moves of the same type, (Same Type Attack Bonus)...
i told the person that i think it was 10-20%, i asked a diffrent person and he said he thinks its +50%,

just wanted to know for sure the next time im asked such a question :s

 

[mondays suck]

It is and has always been 50%.
..how else could level 4 Pidgeys be so frightening at the beginning of the game?