I've looked at the Tanner calculator and it's predicted me at a 3.2. I know that should be enough for me to feel comfortable with the fact I'm hopefully not going to be a midgit 16 year old forever. However, I was wondering if there was a more accurate way of predicting when the penis will grow? I've been with my girlfriend for a year and a half. She wants to have it, and so do I, but as much as I would like to believe "Size doesn't matter" these days a lot of rumors go around, and I don't really want to go the rest of my post 16 days with that kind of rumor following me everywhere I go.
As I write at this time, there are fine hairs on my arms legs and chin and some under my nose. I'm about 5 foot 1 inch. At the moment my penis is 2 inches flaccid and 3.1 inches when hard. I understand if there isn't a more accurate way to measure when it will grow, but I thought it was worth asking.
The penis grows the most in length during stage 3 and you've just started that stage. As your height increases during this stage, your penis will also get longer (measuring the erect length). You'll just have to be patient, but you should see it getting longer over the next year or so.
However, there is an important issue that you've raised that we need to discuss. You talk of having sex with your girlfriend without being committed to her in marriage. That is called "fornication" and is against God's laws. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10). There are good reasons why God wants people to wait until marriage before having sex. If you would like to know some of the reasons, take a look at: Why Sex Outside of Marriage is Wrong.