In short, if you have a 3.0 GPA or better on your US high school transcripts and at least a 1300 SAT or 29 ACT score, you will be accepted to German university. If you don’t meet these requirements, there are still ways to be admitted to university, so I’ll try and give a general overview below.
A lot of the following information (in the form of a fantastically clear and easy to use flow-chart you can click through) can be found on the German Academic Exchange Service (Deutscher Akademischer Austausch Dienst, DAAD) website at https://www.daad.de/deutschland/nach-deutschland/voraussetzungen/en/6017-university-admission-and-requirements/ (for the flow chart, click on the USA in the DAAD admissions database), but here is a short overview:
Requirements for American high school students are:
1. A high school diploma (not a GED), with a 3.0 GPA (or better) and the following classes:
4 credits (years) in English with at least a C, including English 4, honors English, or AP English
2 credits of a second language
3 credits of social studies
5 credits total of math and science with at least a C: math classes include at least two of the following: Algebra 2 or 3, Trigonometry, pre-calc; science classes include at least two of the following: Biology, Chemistry, Physics
2 credits for electives
If you have completed at least a year of college coursework, there are some exceptions to these rules. Click your way through the DAAD admissions database at the address above.
2. Test scores: You are going to need at least an 1150 on your SAT or a 23 on the ACT. If you have at least a 1300 SAT or 29 ACT, then you can start university (providing you know some German, see below). (Seriously, that was easy, right?!) If you have below this, you can be admitted to a Studienkolleg, which is a kind of 1-2 semester long prep course leading to university. The good news is, you can choose courses in the area you want to study later. (Scroll down for more information regarding the Studienkolleg.)
Here, too: if you have completed at least a year of college coursework, or if you have completed AP coursework in the area you want to major in, there are some exceptions to these rules. Click your way through the DAAD admissions database at the address above.
3. Proof of German language abilities: This varies depending on whether you want to study in an English-speaking program (international programme) at the university or a German-speaking one. Some universities have different requirements, unfortunately there isn’t really a pat answer to give here. (Upside: if you don’t speak German or are worried about your language level, you will probably be able to work things out.)
If you have learned German, you can sign up to take an exam which will test your speaking, listening, reading, and writing skills. I won’t lie, these exams aren’t easy. Paired with the general tendency of the German grading system to make it fairly difficult to get a 1 (equivalent of an A) in anything, this means you do have to study for these. The two most common ones are the DaF (Deutsch as a foreign language) and the DSH (Deutsche Sprachprüfung für den Hochschulzugang ausländischer Studienbewerber). You don’t have to come to Germany to take these, they are also offered in the US (or many other countries around the world).
You can take a sample test here to see how you would do: http://www.testdaf.de/teilnehmer/tn-vorbereitung_test.php?id=1
Remember, if you have your heart set on studying in a German program here, you will have to be able to pass a test like this. BUT! even if your result is less than stellar, remember that there is a lot that can be done to improve your language skills if you are willing to work a little. When I got to Germany as part of my exchange year, even despite my high school German with fantastic teachers, I was still far under where I needed to be to pass the exam. I was just never one of those people gifted in languages. But, luckily, language is something you don’t need to be talented in to learn as long as you decide to put in the hours.
Here is helpful information from the DAAD regarding language skills: https://www.daad.de/deutschland/nach-deutschland/voraussetzungen/en/6221-german-language/
As I mentioned above, you can still get a German education and live in Germany but study in an English-speaking program. This is a fairly new option; when I applied 10 years ago it was not on the table, but I have seen it attract several people to Germany each year who otherwise would have stayed away, so it’s quite a good thing for those whose German isn’t yet up to par.
So what if you don’t meet these requirements? Check out whether you can enroll for a Studienkolleg (prep-course) to help you get in.
Here are some helpful links on applying:
DAAD general overview of applying (not extremely clear, but comprehensive): https://www.daad.de/deutschland/nach-deutschland/voraussetzungen/en/6017-university-admission-and-requirements/