Loading please wait

The smart way to improve grades

Comprehensive & curriculum aligned

Try an activity or get started for free

Calculate Missing Sides in Similar Shapes

In this worksheet, students will calculate missing sides in similar shapes.

'Calculate Missing Sides in Similar Shapes' worksheet

Key stage:  KS 3

Year:  Year 8 Maths worksheets

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Interpret Mathematical Relationships Algebraically/Geometrically

Difficulty level:  

Worksheet Overview

Remember, shapes that have the same size angles and are enlargements of each other are called  similar.


Russian dolls


When we enlarge a shape we use a multiplier 

We call it a scale factor


The shapes below are similar!   


similar shapes


We can find the scale factor.

Large height ÷ Small height = 6 ÷ 2 = 3


Large base ÷ Small base = 3 ÷ 1 = 3


Both answers are 3, so the scale factor is 3


We can use this to find any missing sides. Let's try a question.



The shapes below are similar.

Work out the length of the missing side, A.


similar triangles



To find the scale factor, we can divide the heights because we have both.

Scale factor = 12 ÷ 6 = 2


To find base A we can multiply the small base by the scale factor:

5 x 2 = 10

A = 10


Let's try some questions like this!


girl writing

What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started

Try an activity or get started for free

  • National Tutoring Awards 2023 Shortlisted / Parents
    National Tutoring Awards 2023 Shortlisted
  • Private-Tutoring-WINNER-EducationInvestor-Awards / Parents
    Winner - Private Tutoring
  • Bett Awards Finalist / Parents
  • Winner - Best for Home Learning / Parents
    Winner - Best for Home Learning / Parents