A LITTLE PRACTICE, EVERY DAY·GCSE MATHS
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Statistics & Probability · Foundation

Stem & leaf diagrams

A stem-and-leaf diagram organises a data set by splitting each value into a "stem" (the leading digits) and a "leaf" (the final digit). It keeps all the original data while making the distribution clear.

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Revising stem & leaf diagrams the night before an exam? These are condensed revision notes — the facts, formulas and mistakes examiners actually mark, with no long explanations. Prefer a full walkthrough with step-by-step reasoning instead? Search “Stem & leaf diagrams GCSE” on the site for the complete guide.

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Key facts to remember

  • 1Stems go on the left, leaves on the right.
  • 2Leaves should be listed in order smallest to largest.
  • 3Always include a key, e.g. "2 | 4 means 24".
  • 4The median is easy to find by counting in from the ends.
  • 5Back-to-back stem-and-leaf diagrams compare two data sets on the same stems.
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Worked examples

Example 1

Draw a stem-and-leaf diagram for: 22, 31, 18, 25, 27, 19, 34, 23, 28.

Working

  1. Stems: 1, 2, 3.
  2. Stem 1 → leaves 8, 9
  3. Stem 2 → leaves 2, 3, 5, 7, 8
  4. Stem 3 → leaves 1, 4
  5. Add key: 2 | 5 means 25.
AnswerRows: 1 | 8 9 ; 2 | 2 3 5 7 8 ; 3 | 1 4. Key: 2 | 5 = 25.
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Common mistakes

✗Forgetting the key — you lose a mark.
✗Leaves out of order.
✗Using two-digit leaves.
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Exam tips

✓Always add a key.
✓Order the leaves smallest to largest.
✓To find the median, count in from both ends simultaneously.

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