How can you measure the circumference of a circle?

Depending on the everyday situation, there are different methods of measuring the size of a circle with simple means, i.e. objects that you have in the household. By the way: Do you know the radius or Diameter of the circle, all the methods presented allow an approximation for the circle number Pi (about 3.14) to be obtained.

Determine the circumference of a circle with tools

• If the circle is available, for example, in the form of a pipe cross-section or a cylinder surface, it is advisable to to use a flexible measuring tape (tailor's equipment) and to put it around the round body at the same height place. Read the circumference of the circle on the measuring tape. Alternatively, you can use a rope, string or thread for this task - depending on the thickness of the object. Then measure the length of the string you need on a folding rule or ruler.
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• Some circles can be rolled, for example wheels or other round objects. Use a pen to mark the start of your rolling process on the circumference of the circle and roll the circle or the round body back up to this mark. Measure the roll-off distance with a tape measure.
• But what if the circle is on paper? In this case, you can take a twisted thread, moisten it and use it to cover the entire circumference of the circle as much as possible. Then all you have to do is measure the length of the thread required for this. By the way, moistening helps that the thread stays in place and is less likely to slip. However, some care is required.

How to measure the circumference with "pieces of cake"

1. With this method, the circumference of the circle is straightened (in the desired approximation) and thus measurable. You don't have to do much more than cut the circle, for example on paper, into as many segments as possible - similar to how you cut a cake into individual pieces.


Formula for diameter - this is how you convert the circumference

Sometimes simple things cause headaches: You have a given circumference ...

2. Now place the individual sections of the circle alternately in opposite directions so that an almost straight part of the circumference of one piece comes to the tip of the next piece of cake.
3. This creates a rectangle. The width of this rectangle corresponds to the radius of the circle, the length is just half the circumference and can easily be measured with a ruler.
4. Of course, the more "pie pieces" you cut out of the circle, the more precise the method.
5. One knows the circumference U of the circle using this method. so the area of ​​the circle results as a rectangular area.