What is Diagram Completion in IELTS Reading?

Diagram Completion asks candidates to label parts of a visual — a scientific diagram, map, technical drawing, or process flow-chart — using words taken directly from the reading passage. A word limit is always specified. The visual represents something described in the passage, and your task is to match labelling words to specific parts of the diagram by reading the relevant passage section.

What types of diagrams appear in IELTS Reading?

Three types appear: (1) Diagram labelling — label parts of a scientific or technical drawing (e.g. cross-section of a cell, anatomy of a machine); (2) Map completion — label locations or features on a map (more common in General Training); (3) Flow-chart or process diagram completion — fill stages of a process sequence described in the passage. Each type requires locating the relevant passage section and extracting exact words within the word limit.

Do diagram completion answers follow passage order?

Generally yes for flow-charts and process diagrams — the stages of the process are usually described in chronological sequence in the passage, and the flow-chart follows the same sequence. For diagram labelling and map completion, the passage section describing the diagram is usually a contiguous block, but the specific labels may not appear in strict left-to-right or top-to-bottom order. Locate the diagram description section first, then search within it.

Can I use numbers in diagram completion answers?

Only if the instruction specifies 'AND/OR A NUMBER'. A typical instruction reads 'NO MORE THAN TWO WORDS AND/OR A NUMBER FROM THE PASSAGE'. If the correct answer is a measurement like '3.7 metres', the number counts as one word unit. If the instruction says 'NO MORE THAN TWO WORDS' without specifying numbers, a number written as a digit is still typically accepted, but a number written out as a word (e.g. 'three') counts toward the word limit.

What if I cannot find the diagram section in the passage?

Look for signal language that introduces descriptions or processes: 'as shown in Figure 1', 'the structure consists of', 'the process begins when', 'moving from left to right'. Also look for the specific labels or part names already visible in the diagram — scanning for those exact words in the passage will take you directly to the relevant section. If the diagram includes any pre-filled labels, use those as anchor scanning terms.

How much time should I spend on diagram completion?

Budget approximately 60–90 seconds per gap, the same as other question types. Diagram completion is not inherently slower than other question types — the visual element can actually help because it shows you exactly what part of the passage to find. The main time risk is spending too long trying to understand the diagram before locating the passage section. Locate the passage section first; the diagram context will make sense once you are reading the right text.

Reading10 min read·Updated June 5, 2026

IELTS Reading Diagram & Flow-Chart Completion: A Visual Step-by-Step Guide

How to locate the passage section describing a diagram, fill gaps within word limits, and handle all 3 diagram types: labelling, map, and flow-chart.

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IELTS Reading diagram completion strategy for labelling, maps and flow-charts

Written by mockDe Editorial Team· IELTS preparation specialists

Last Updated June 5, 2026

10 min read

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Key Takeaways

Locate the passage section describing the diagram before attempting to fill any gaps.
Copy exact words from the passage — within the stated word limit.
Use pre-filled diagram labels and visible part names as scan anchors in the passage.
For flow-charts, answers usually follow the chronological order of the process described.
The diagram itself is a comprehension aid — use its structure to predict what type of word fills each gap.

How do I answer Diagram and Flow-Chart Completion questions in IELTS Reading?

Diagram and flow-chart completion requires finding the passage section that describes the visual, then extracting exact words within the stated word limit to fill each gap. The diagram is not separate from the passage — it is a visual representation of information described in the text. Your task is to bridge between the visual layout and the passage language.

Find the passage section describing the diagram — look for signal phrases like 'as shown' or 'the process begins'
Use any pre-filled labels in the diagram as scanning anchors in the passage text
For flow-charts: answers follow the described process sequence in the passage
Check your word count before writing — exceeding the limit scores zero

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Part of the IELTS Reading cluster

IELTS Reading: The Complete Blueprint

What is Diagram & Flow-Chart Completion?

An IELTS Reading question type in which candidates complete a visual — a diagram, map, or flow-chart — by filling gaps with words taken directly from the reading passage. A strict word limit applies. The visual represents a process, structure, or location described in the passage text.

Unlike Matching Headings or True/False/Not Given, Diagram Completion is one of the least frequently appearing question types. It appears in roughly one in three Academic Reading papers, often in Passage 3.

What Is Diagram & Flow-Chart Completion?

In a Diagram Completion task, you are given a visual representation — a cross-section diagram, a process flow-chart, a map — alongside a reading passage that describes the same subject. The diagram has gaps with arrows pointing to specific parts or stages. Your job is to fill each gap with words taken directly from the passage.

The visual element is intentional: it tells you something about the type of word you need. An arrow pointing to a component of a machine likely needs a noun (the name of the component). A box in a process flow-chart likely needs a verb or noun describing what happens at that stage.

The fundamental challenge is that many candidates try to understand the entire diagram before reading the passage, which is inefficient. The passage is the primary source — the diagram is a map telling you what information to find.

The 3 Types of Diagram Questions

1. Diagram Labelling

Label specific parts of a technical or scientific drawing. Common subjects include anatomy, machinery, architectural cross-sections, or geological structures. The passage contains a descriptive section identifying each part. Answers are usually nouns — part names copied directly from the text.

2. Map Completion

Label locations, routes, or features on a map or plan. More common in General Training Reading. The passage describes the geography or layout; you match description to location. Watch for directional language in the passage (north of, adjacent to, between) to orient your answer.

3. Flow-Chart / Process Diagram

Fill stages in a sequential process. The process is described in the passage in chronological or logical order, and the flow-chart mirrors that sequence. Answers are often verbs or verb phrases describing what happens at each stage. This is the most commonly tested diagram type in Academic Reading.

Step-by-Step Method

1. Read the word limit instruction first

Before looking at the diagram. Write the word limit in the margin. Checking it after answering is too late.

2. Scan the diagram — understand its structure

Spend 30–45 seconds understanding what the diagram represents. Is it a machine? A biological process? A map? Note any text already visible in the diagram (labels, stage names, arrows) — these are your scanning anchors.

3. Locate the diagram description section in the passage

Look for the paragraph or section that describes what the diagram shows. Signal language: 'as illustrated', 'the process begins', 'Figure 1 shows', 'moving from left to right'. Alternatively, scan for a pre-filled label from the diagram — it will appear verbatim in the passage.

4. Read the relevant passage section carefully

Read the identified section in full. Map the passage language to the diagram structure: which sentence describes the component with gap 1? Which sentence describes the stage with gap 2?

5. Fill gaps using exact passage words

Copy the exact words from the passage. Do not paraphrase or change word form. Verify that your answer fits grammatically with any surrounding text in the diagram box.

6. Count your words before finalising

Count every word in each answer. If you exceed the limit, identify which word can be dropped without losing meaning.

Word Limit Rules

The word limit for diagram completion follows exactly the same rules as sentence completion. Each word counts separately, including articles and prepositions. Hyphenated words count as one word. Numbers written as digits count as one word unit when the instruction specifies 'AND/OR A NUMBER'.

One additional trap in diagram completion: if the gap already has a partial word visible in the diagram (for example, a suffix like '-ing' or a prefix), that visible text does NOT count toward the word limit — it is part of the diagram structure, not your answer. Read the instructions carefully to understand exactly what you must provide.

Flow-Chart Specific Strategy

Flow-charts test your ability to follow the sequence of a process. The good news: process descriptions in passages follow a predictable structure. Look for temporal and causal sequence language: first, then, next, subsequently, following this, as a result, finally.

Find the sentence that describes the first stage of the flow-chart in the passage — it is usually the first sentence of the process-description section. Then read sequentially forward in the passage, matching each passage sentence to the corresponding flow-chart box. The answers will appear in the same sequence as the flow-chart stages.

For flow-chart gaps, predict the word type from the box's position: a box at the start of a sequence likely needs a verb (what starts the process), a box in the middle needs what happens as a result of the previous stage, and a final box often needs the outcome or end product.

Worked Example

Passage excerpt (process description):

"The desalination process begins when seawater is drawn through intake screens that filter out large debris. The filtered water then passes through a pre-treatment stage where suspended particles are removed using coagulation chemicals. Under high pressure, the pre-treated water is forced through semi-permeable membranes, separating fresh water molecules from dissolved salts. The resulting brine concentrate is discharged back into the ocean, while the purified water undergoes post-treatment mineralisation before distribution."

Flow-chart gap (NO MORE THAN TWO WORDS):

Seawater drawn in → filtered by intake screens → suspended particles removed by ___ → forced through membranes → brine discharged → purified water mineralised

✗Wrong: "chemical coagulation" — word order reversed from passage; may not be accepted.

✓Correct: "coagulation chemicals" — two words, exact passage phrase, fits the gap grammatically.

Practise diagram completion with real IELTS passages

Apply the locate-then-fill method on a full timed reading test. Diagram questions reward systematic readers — randomness is the only mistake.

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