Is it common for games to get a anime? A lot of anime are based off of the plot of a manga and/or light novels. Sometimes an anime is an original work that gets a manga story afterwards, but that isn't always the case.

I remember watching Amagami, where you could obviously notice that it was based on a game, and some are even named after the games such as Final Fantasy.

So how common is it for a anime to be based of a game? I have only seen it once or twice but is it really that uncommon? Or are they just animated in a way that you won't directly notice that it comes from a game unless you already know so?
Just like in this answer, let's take a look at /u/homu's data. 



This basically answers your question right here: between 8% and 15% (avg. 10%) of anime in each year from 2000-2013 were based on a video game of some variety. Games are a minor but not insignificant source for anime. 

Now, if you're asking "what percentage of video games get turned into an anime", the answer almost certainly rounds to 0%. There are a lot of video games out there (probably in the high hundreds per year, at least), but less than 200 anime per year, only a fraction of which are based on video games.

This data set only covers TV anime (thus excluding ONAs, OVAs, and films), but I see no reason to expect that an unusually large percentage of any of those media would be based on games.