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What Is Perimeter and Circumference?

Imagine a pool. The size of the pool depends on how long the sides of the pool are. If you measure all the sides of the pool and add them together, you find the perimeter of the pool, which tells you how far it is to walk around the pool. If the pool is round, we call the perimeter its circumference.

Perimeter of a swimming pool

Think About This

Can you find the circumference of one of the round plates in your kitchen cabinet?

This is not easy to do with a ruler, but using a string is a good idea! Turn the plate upside down. Put the string up to the edge of the plate and drag it around until it meets itself again. Cut the string where it meets itself and stretch out the piece of string that was left around the plate. When you measure the length of that piece of string, you have found the circumference of the plate!

Circumference of circle explanation

All two-dimensional (flat) figures have a perimeter you can measure. The trick with the string is the easiest to use when you come across figures that have uneven sides. In other cases, there are formulas to use that you will learn later. Here are some pictures of different figures and their circumference.

A flat football

Planet, sun and moon

Math Vault

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