IELTS Process Diagram: Band 9 Model Answer, Structure and Vocabulary

Aswathy Mohandas

03/11/2026

9 min read

An IELTS process diagram question asks you to describe the stages of a process, such as how something is made or how a natural cycle works, in at least 150 words, in about 20 minutes. The answer that scores highest has four short paragraphs: a paraphrase of the question, an overview that says how many stages there are and where the process begins and ends, and two paragraphs that take the reader through every stage in order, mostly in the passive voice.

This guide shows you that structure, walks through a sample process diagram question with a full model answer written to the Band 9 descriptors, explains why the answer meets each of the four marking criteria, and gives you the sequencing words and passive forms you need. All of it applies to IELTS Academic Writing Task 1.

What is a process diagram question in IELTS Writing Task 1?

In IELTS Academic Writing Task 1 you describe visual information in your own words. According to the official IELTS Academic Writing format page, that can be a graph, chart or table, or a diagram of an object, device, process or event. You must write at least 150 words in about 20 minutes, in full sentences, not notes or bullet points. Task 1 is worth one third of your Writing band; Task 2 is worth two thirds.

A process diagram shows a series of steps, usually with arrows, pictures and short labels. There are two kinds. A man-made process shows how something is produced or treated, such as how bricks are made or how water is cleaned. A natural process shows something that happens in nature, such as the life cycle of an insect or the water cycle. Unlike a line graph, a process diagram has no numbers to compare, so your score depends on describing every stage clearly, in the right order, with accurate grammar.

How do you structure a process diagram answer?

Use four paragraphs. This layout makes your answer easy to follow, which is part of the Coherence and Cohesion score.

1. Introduction (one sentence). Paraphrase the question: what the diagram shows and what the process produces. Do not copy the question word for word.
2. Overview (one or two sentences). Say how many stages there are, where the process starts and where it ends, and whether it is a straight line or a cycle that repeats. Mention any by-product or branch. The band descriptors ask for a clear overview at Band 7 and at least an attempted one at Band 6.
3. Detail paragraph 1. Describe the first half of the stages, in order, using the labels on the diagram.
4. Detail paragraph 2. Describe the remaining stages through to the end of the process.

Split the stages where the diagram naturally divides, for example where the material moves from one place to another or where it changes form. Every stage should appear in your answer: unlike a chart, a process has no “minor figures” you can safely leave out, although you can skip small details inside a stage.

Sample IELTS process diagram question

The question below is an original practice task written by Galvanize. The process and its details are written for practice.

The diagram below shows how used cooking oil from restaurants is turned into biodiesel fuel. Summarise the information by selecting and reporting the main features, and make comparisons where relevant. Write at least 150 words.

The diagram shows eight stages, each with a picture and a label:

Before you write, spend two or three minutes reading the diagram from start to finish. Here is the story: the process is a straight line, not a cycle; it begins at restaurants and ends at filling stations; the oil is cleaned, then chemically changed, then cleaned again; and one by-product, glycerine, leaves the process at stage 6.

Band 9 model answer: process diagram

This model answer was written to meet the Band 9 descriptors. It is 190 words. No one can guarantee an examiner’s score, but every feature that the top band asks for is here.

The diagram illustrates the stages by which used cooking oil from restaurants is converted into biodiesel fuel.

Overall, the process is linear and consists of eight stages, beginning with the collection of waste oil and ending with the delivery of fuel to filling stations. Along the way, the oil is cleaned, chemically treated and then cleaned again, and one by-product, glycerine, is removed.

To begin with, used oil is collected from restaurants in sealed drums, which are then transported by lorry to a processing plant. On arrival, the oil is passed through a fine filter so that any food particles are removed, after which it is heated to 60°C in order to drive off the remaining water.

Next, the warm oil is mixed with methanol and a catalyst in a reaction tank, where it is left for six hours. During this time, the mixture separates into two layers: the lighter biodiesel rises to the top, whereas the heavier glycerine sinks and is drained off to be sold to soap manufacturers. The biodiesel is subsequently washed with water and dried, before finally being stored in tanks and delivered to filling stations.

Why does this answer meet the Band 9 descriptors?

Examiners mark Task 1 on four criteria, each worth a quarter of the task score. The table below sets the answer against the Band 9 wording in the official IELTS Writing band descriptors (updated May 2023).

To see how your four criterion scores turn into a Writing band, and how Writing combines with the other sections, read our guide to IELTS band scores.

What vocabulary do you need for a process diagram?

A process answer is held together by two things: words that show the order of the stages, and passive verbs that describe what is done at each one. Repeating “then” at every stage is the most common reason a good answer loses Coherence and Cohesion marks.

Use the present simple passive for most stages, because the focus is on what happens to the material, not on who does it:

• Present simple passive: the oil is heated; the drums are transported.
• With a modal: the mixture must be left for six hours; the fuel can be stored for several months.
• After a sequencer: once the water has been removed, the oil is mixed with methanol.
• Active where nothing is done to it: the mixture separates; the lighter liquid rises. Some verbs describe what a substance does by itself, so they stay active.

Useful process verbs include collect, transport, deliver, filter, sieve, crush, grind, heat, cool, boil, mix, add, pour, separate, drain off, wash, dry, store and package. For a natural cycle, you will also need verbs such as develop into, grow, emerge, evaporate, condense and return to.

For a wider word list beyond Task 1, see our IELTS vocabulary guide.

How do you describe a natural cycle instead?

Natural processes, such as the life cycle of a frog or the water cycle, usually go round in a circle instead of running from a start to an end. Three things change in your answer:

• The overview says it is a cycle and names its main phases, for example “the life cycle consists of four main stages, from egg to adult, and then begins again”.
• The verbs are mostly active, because nobody is doing anything to the animal or the water: eggs hatch, tadpoles develop into frogs, water evaporates.
• The end links back to the start: “the adult then lays eggs, and the cycle is repeated”.

Which mistakes lower a process diagram score?

• No overview. Band 6 for Task Achievement needs a relevant overview to be attempted, and Band 7 needs a clear one. Say how many stages there are and where the process begins and ends.
• Skipping stages. Each stage is a main feature of a process. Leaving one out means the task is not fully covered.
• Copying the labels. Labels such as “oil heated to remove water” are notes. Turn them into full passive sentences in your own words.
• Using only the active voice. “Workers collect the oil and they put it in drums” adds people who are not on the diagram and misses the grammar range the task invites.
• Explaining or judging the process. Saying biodiesel is “better for the environment” adds information that is not in the diagram.
• Writing under 150 words. A short answer loses Task Achievement marks. Aim for 160 to 190 words.

Maps are the other diagram type in Task 1, and they also need careful use of the passive to describe changes over time; see our guide to IELTS maps. When you can write a process answer in 20 minutes, test yourself on a full paper with our free IELTS mock test, and work out your overall band with the IELTS band score calculator.