Angles in a triangle

A teacher-created worksheet to support KS2 maths learning and help your Year 6 child practise calculating angles in a triangle.

The three inside angles in a triangle always add up to 180 degrees. Can you work out what the following angles are, WITHOUT a protractor?

How do you calculate angles in a triangle?

Calculating angles in a triangle can seem tricky at first, but it’s actually quite simple once you understand the basic rules! 

• A triangle is a shape with three sides and three angles.
• The most important thing to remember is that the three angles inside any triangle always add up to 180 degrees. This is a key fact that will help in calculating any missing angles.
• If you know two angles in a triangle, you can easily find the third one.
• For example, let’s say your child knows two angles: 50 degrees and 60 degrees.
• You can find the missing angle by subtracting the sum of these two angles from 180 degrees.

What are the different types of triangles in Year 6 maths?

• Equilateral triangle: All three angles are the same, and each one is 60 degrees (since 180 degrees divided by 3 is 60).
• Isosceles triangle: Two angles are the same, and you can find the third angle using the same subtraction method.
• Scalene triangle: All three angles are different, but they still add up to 180 degrees.

How will this KS2 worksheet help your child at home?

This simple but effective KS2 activity was designed by an experienced primary school teacher and will help your child understand how to calculate the missing angle in a triangle. They are encouraged to have a go themselves and answers are provided. 

For more help with Shape and Space, check out our hub page, or try a new challenge such as our Finding unknown angles in quadrilaterals worksheet.