IELTS test scores range from 1-9 where 1 means a non-user and 9 means an expert. There is also a 0 score which means not attempted. 

According to the British Council, score 9 implies that you are an expert in English. As you come down, the value of the counts also diminishes. For example, rating 8 would indicate very good and score four would mean limited/average. 

Scores are also given in .5 bandwidths. For example, 7.5 is a very good score, and so on. 

The scores are expressed in the form of bands

A band one refers to a non-English user. This means that the person has no idea about English grammar, punctuation or even framing sentences.

However, a band seven would mean that the person is an expert in English. So each step from 1- 9 have different levels of English. The overall band score is calculated by taking the average of all four sections you scored in an IELTS.

The average of all these scores would be your band score. 

A good score on IELTS depends on the institution you apply to. Different institutes have different requirements. In the case of colleges and universities, a score of 5.5 to 7.5 is usually considered a good score. 

In the case of reading and listening, the scoring is quite straightforward. For example, if you get 30 questions correct out of 40, then for a General exam the band score will be six, and for an Academic exam, the band score jumps to a 7. 

The writing section is slightly different to grade. 

The scores are calculated using a  detailed rubric.  The important keys the examiner looks for is coherence and cohesion, Lexical Resource, Grammatical range, Task achievement and task response.