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What are regular and irregular shapes?

What are regular and irregular shapes?
We explain what regular and irregular shapes are and suggest mnemonics to help children remember how many sides different shapes have. We also have examples of the types of questions primary-school children might be asked about shapes.

What are regular and irregular shapes?

Regular shapes have sides that are all equal and interior (inside) angles that are all equal.

Irregular shapes have sides and angles of any length and size.

Here are various different shapes in regular and irregular forms:

Regular pentagon, regular hexagon, regular octagon

Irregular pentagon, irregular hexagon, irregular octagon

Learning about shapes: number-of-sides mnemonics

Children in Key Stage 2 learn lots of facts about polygons and need to know how many sides a pentagon, hexagon and octagon have. A few tips to help them remember:

  • A good way to help them remember this, is to show them a picture of the Pentagon building in America and get them to count the sides.
  • A teacher may point out that a hexagon has an 'x' in it, as does the word 'six', which is how many sides it has.
  • An octagon has eight sides, just as an octopus has eight legs.

Children need to be aware that ANY shape with five sides is a pentagon, just as ANY shape with six sides is a hexagon and ANY shape with eight sides is a hexagon. They can get very used to just seeing the shape in its regular form, but need to be reminded of the irregular versions as well.

Children may be asked a question similar to the following:

Put a tick on the two octagons:

(The third and fourth shapes are octagons.)


As they move up Key Stage 2, they may be asked to think about various properties of a group of shapes and then complete a table, for example:

Look at these shapes and then fill in the table. The first one has been done for you:

This is the completed answers table:

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