What is a nonagon?
A nonagon is a flat shape with nine straight sides and nine corners.
The answer
A regular nonagon has 9 sides, 9 vertices, no parallel sides and 9 lines of symmetry. The angles inside a nonagon add up to 1260°.
Nonagon diagram and properties
| Property | Regular |
|---|---|
| Sides | 9 |
| Vertices (corners) | 9 |
| Angles add up to | 1260° |
| Each angle | 140° |
| Right angles | 0 |
| Pairs of parallel sidesIrregular nonagons can have some. | 0 |
| Lines of symmetryAn irregular nonagon may have fewer. | 9 |
Key facts about the nonagon
- The angles inside any nonagon add up to 1260°.
- In a regular nonagon every angle is 140°.
- A regular nonagon has no parallel sides, because it has an odd number of sides.
- It is also called an enneagon, from the Greek for nine.
Where you see it
Nonagons are rare in everyday life, which is exactly why they turn up in 11+ questions: a child has to use the angle rule rather than remember a fact.
The common mistake
Mixing up nonagon (9 sides) and decagon (10 sides). "Non" is from the Latin for ninth; "dec" is ten, as in decade.
An 11+ style question
What is the size of each angle in a regular nonagon?
Answer: 140°
- The angles add up to (9 − 2) × 180 = 1260°.
- A regular nonagon has 9 equal angles, so 1260 ÷ 9 = 140°.
Related shapes and skills
More shapes
Questions parents ask
How many sides and vertices does a nonagon have?
A nonagon has 9 straight sides and 9 vertices (corners). Its angles add up to 1260°.
How many lines of symmetry does a nonagon have?
A regular nonagon has 9 lines of symmetry. An irregular nonagon may have fewer.
Is a nonagon the same as an enneagon?
Yes. Both words mean a shape with nine sides. Nonagon is the one used in UK schools and 11+ papers.
Shape questions are quick marks in the 11+
Angles, symmetry, nets and 3D shapes come up in 11+ maths and non-verbal reasoning. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.