I think your best bet would be IELTS website itself.
It states the following:
Listening and reading
IELTS Listening and Reading papers contain 40 items and each correct item is awarded one mark; the maximum raw score a candidate can achieve on a paper is 40. Band scores ranging from Band 1 to Band 9 are awarded to candidates on the basis of their raw scores.
Although all IELTS test materials are pretested and trialled before being released as live tests, there are inevitably minor differences in the difficulty level across tests. In order to equate different test versions, the band score boundaries are set so that all candidates’ results relate to the same scale of achievement. This means, for example, that the Band 6 boundary may be set at a slightly different raw score across versions.
The tables below indicate the mean raw scores achieved by candidates at various levels in each of the Listening, Academic Reading and General Training Reading tests during 2006 and they provide an indication of the number of marks required to achieve a particular band score.
Listening
| Band score | raw score out of 40 |
| 5 | 16 |
| 6 | 23 |
| 7 | 30 |
| 8 | 35 |
General Reading
| Band score | raw score out of 40 |
| 5 | 15 |
| 6 | 23 |
| 7 | 30 |
| 8 | 34 |
The Academic and General Training papers are graded to the same scale. The distinction between the two modules is one of genre or discourse type. Academic papers may contain source texts featuring more difficult vocabulary or greater complexity of style. It is usual that, to secure a given band score, a greater number of questions must be answered correctly on a General Training Reading paper.
Writing and speaking
When marking the Writing and Speaking sub-tests, examiners use detailed performance descriptors which describe written and spoken performance at each of the 9 IELTS bands.
Writing
Examiners award a band score for each of four criterion areas: Task Achievement (for Task 1), Task Response (for Task 2), Coherence and Cohesion, Lexical Resource and Grammatical Range and Accuracy. The four criteria are equally weighted.
Speaking
Examiners award a band score for each of four criterion areas: Fluency and Coherence, Lexical Resource, Grammatical Range and Accuracy and Pronunciation. The four criteria are equally weighted.
Versions of the band descriptors for Writing and Speaking have been developed to help stakeholders better understand the level of performance required to attain a particular band score in each of the criterion areas. IELTS examiners undergo intensive face to face training and standardisation to ensure that they can apply the descriptors in a valid and reliable manner.
