This article is extracted from IELTS Scores Explained published by Cambridge ESOL in early 2009.

You can also read the original text from IELTS | Researchers - Score processing, reporting and interpretation.

Some alterations, which are made by Mr. Tea, are set to make the candidates understand the IELTS scoring system more effectively.

All IELTS marking takes place at the test centre by trained markers and examiners.

Markers are trained to understand the IELTS marking policy and are required to demonstrate that they are marking to standard before they are allowed to mark Listening and Reading papers. Markers are re-tested every two years to ensure that their marking remains up to standard. Systematic monitoring and double marking of a proportion of answer sheets is carried out at each administration.

Examiners for the Writing and Speaking sub-tests are recruited and trained in line with agreed standards. They are required to demonstrate that they are marking to standard every two years in addition to on-going monitoring of their performance.

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.

Overall Band Score

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).

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 and 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.

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.

Since each Academic or General Training Writing contains two tasks – Task 1, Task 2. Each task is assessed independently. The assessment of Task 2 carries more weight in marking than Task 1. See the following table, the first horizontal line reports Bands of Task 2 a candidate may experience, vise versa, the very left vertical line reports Bands of Task 1 one can obtain:

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.

More details relating to this please read Detailed Description of IELTS Speaking Band Scores by a former IELTS Speaking Examiner.