This is the best place to start! From this page, you can find out what the CEFR Levels are and what they mean. You can also take the level tests below to see what your current CEFR English level is. There is a grammar test, a vocabulary test and a reading test.
The CEFR levels range from Level A1 (Beginner) to Level C2 (Proficient). Knowing where you are on the CEFR scale can really help you know what you need study and how to improve.
It’s a good idea to take this test once, then come back again in about 4 weeks and try it again. See if your score improves!