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⭕ Circumference and Area of Circles

Meet pi, the number hidden in every circle, and use it to measure the distance around a circle (C = πd) and the space inside it (A = πr²).

2
lessons
~15 min
to learn
🔢 Math
subject
Teens
level
Start the course →

What you’ll learn

  1. Around a Circle: CircumferenceIdentify the parts of a circle, understand pi, and calculate circumference using C = πd.A circle's radius reaches from the centre to the edge and its diameter crosses through the centre, so d = 2r. Dividing any circle's circumference by its diameter always gives pi (π ≈ 3.14). This gives the circumference formula C = πd, the same as C = 2πr. For a diameter of 10 cm, C ≈ 31.4 cm.
  2. Inside a Circle: AreaCalculate the area of a circle with A = πr² and choose between area and circumference.The area of a circle is the space inside it, found with A = πr²: square the radius, then multiply by pi. A radius of 5 cm gives an area of about 78.5 cm². Circumference and area are different measures — circumference is a distance in plain units while area is a surface in square units — so it's important to pick the right formula for each task.

Questions this course answers

How does the diameter of a circle relate to its radius?

The diameter crosses the whole circle through the centre, so it is always twice the radius: d = 2r.

What does pi (π) represent?

Pi is the constant ratio of any circle's circumference to its diameter, about 3.14159.

What is the formula for the area of a circle?

The area of a circle is pi times the radius squared: A = πr².

A circle has radius 5 cm. Using π ≈ 3.14, what is its area?

A = πr² = 3.14 × 5² = 3.14 × 25 ≈ 78.5 cm².

You need to buy edging to go around a circular flower bed. Which do you calculate?

Edging runs along the boundary, which is the distance around the circle — its circumference.

Grounded in trusted sources

  • Khan Academy — area and circumference of circles
  • National Council of Teachers of Mathematics
  • BBC Bitesize — circles
  • Britannica — pi

Every Wunder lesson is built from real, reputable sources — never invented.

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⭕Parts of a Circle🔷All About 2D and 3D Shapes📐Classifying Angles and Shapes📏Classifying Shapes by Their Lines🕐Clockwise and Counterclockwise Turns🪙Coins and Their Values⚖️Comparing Fractions⚖️Comparing Fractions and Decimals

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