Circumference of a Circle
The circumference of a circle is the length of its curved boundary.
In one line: Circumference is the circle's outside boundary.
Practice This ConceptUnderstand it
A circle has no straight sides, so its perimeter is called circumference. It depends on the radius or diameter and uses π, written as π.
Example
Formula and rule
C = 2πr or C = πd, where r is radius and d is diameter. π is irrational and is often approximated as 22/7 or 3.14.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1A wheel has radius 21 cm.
- 2One full rotation covers its circumference: 2 × 22/7 × 21 = 132 cm.
Method you can reuse
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
What is the circumference of a circle with diameter 14 cm using π = 22/7?
Think first, then show answerHide answer
Common wrong answer
154 cm for radius 7 cm.
Why it loses marks: It is area, not circumference.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
The circumference of a circle is the length of its curved boundary.
- 2
Add for 2 marks
Example: For radius 7 cm, circumference = 2πr = 2 × 22/7 × 7 = 44 cm.
- 3
Add for 3 marks
A circle has no straight sides, so its perimeter is called circumference.
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