When asking for a raise, how do you guys know, how much to ask for / how much are you worth?

I've been working as a programmer for the last year and a half, and it's my first real gig in the sector. Without getting into much details, I've currently the opportunity to ask for a raise, but I don't know what would be an appropriate amount or how to research or calculate it.
Any input would be very much appreciated.

"Don't learn Frameworks, learn techniques."

1) Keep improving Java skills
2) Keep learning Python
3) Learn Docker
4) Finally use my Raspberry Pi

First job. Started 2 weeks ago, I'm doing an internship in a Web development company and even though my studies were mainly for Java and Android, it's going fine.
Past week I learnt to use .less and HTML5 and will start with Javascript now.

Fuck Threads and fuck multithreading in general.
I've spent the last 2 hours and a half looking for an important error that did my project not work at first execution, and it was all because I did start a side Thread, but forgot to wait until it was done before showing the output of it.

Fucking multithreading...