- Definition
The diameter is a straight line that goes from one side of a circle to the other, passing right through its middle.
If a circle has a radius of 5 cm, its diameter is a 10 cm line passing through the center.
How to teach this in 30 seconds
Try this analogy: The diameter is like the longest straight cut you can make across a pizza, as long as your cut goes right through the very center.
Ask your child: How could you find the widest part of this plate using just a ruler?
Common mix-up: Kids may think any line that crosses a circle is a diameter. The diameter must be the longest possible straight line, and it has to pass directly through the center.
Examples
- The diameter of a bicycle wheel is the distance from one point on the rim to the opposite point, passing straight through the middle hub.
- Measuring the width of a circular dinner plate straight across its center gives you its diameter.
diameter is a term used in Ontario’s Kindergarten to Grade 8 curriculum.
Where this shows up
The descriptions on this page are SmartStudy’s own original, plain-language writing — not the Ministry’s wording. They are aligned to the Ontario Curriculum, © King’s Printer for Ontario. For the Ministry’s official wording, see the source link below. SmartStudy is an independent service and is not affiliated with, endorsed by, or sponsored by the Government of Ontario or the Ministry of Education. Ontario Curriculum and Resources ↗
