IELTS is scored on a scale of 0 to 9. A band is given to the test taker in each component of the proficiency test. An overall score is also given, which is the average of the four components or modules.
Writing
The language parameters are Task Achievement (Task-1)/Response (Task-2), Coherence and Cohesion, Grammatical Range and Accuracy, and Lexical Resource. Each of these is scored out of 9, and then the average for each task is used.
The final writing score is calculated by adding the marks for task 2 twice and task 1 once; the average of three scores is the final band. E.g., For 6.0 in task 1 and 7.0 in task 2, the overall Writing score of 20/3 would be band 6.5.
Listening
Forty questions are divided so that nine band structure is used for scoring. The public version of the conversion table is available.
Reading
Forty questions are divided so that nine band structure is used for scoring. The public version of the score conversion table is available.
Speaking
The language parameters based on which Speaking is scored are fluency and Coherence, Grammatical Range and Accuracy, Lexical Resource, and Pronunciation. Each of these is scored out of 9, and then the average score is used.