Candidates receive scores on a Band Scale from 1 to 9. A profile score is reported for each skill. The four individual scores are averaged and rounded to produce an Overall Band Score. Overall Band Scores and scores for each sub-test (Listening, Reading, Writing and Speaking) are reported in whole bands or half bands.

Candidates receive a Test Report Form setting out their Overall Band Score and their scores on each of the four sub-tests: Listening, Reading, Writing and Speaking. Each of the sub-test scores is equally weighted. The Overall Band Score is calculated by taking the mean of the total of the four individual sub-test scores.
Overall Band Scores are reported to the nearest whole or half band. For the avoidance of doubt, the following rounding convention applies; if the average across the four skills ends in .25, it is rounded up to the next half band, and if it ends in .75, it is rounded up to the next whole band.
Thus, a candidate achieving 6.5 for Listening, 6.5 for Reading, 5.0 for Writing and 7.0 for Speaking would be awarded an Overall Band Score of 6.5 (25 ÷ 4 = 6.25 = Band 6.5).
Likewise, a candidate achieving 4.0 for Listening, 3.5 for Reading, 4.0 for Writing and 4.0 for Speaking would be awarded an Overall Band Score of 4.0 (15.5 ÷ 4 = 3.875 = Band 4.0).
On the other hand, a candidate achieving 6.5 for Listening, 6.5 for Reading, 5.5 for Writing and 6.0 for Speaking would be awarded band 6 (24.5 ÷ 4 = 6.125 = Band 6).

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.

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.

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.

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.
To view a version of the descriptors for Writing Task 1 at: http://www.ielts.org/pdf/UOBDs_WritingT1.pdf

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.
To view a version of the descriptors for Speaking at: http://www.ielts.org/pdf/UOBDs_SpeakingFinal.pdf