- 1). Measure the circumference of a circle using a piece of string. The string should be as thin as possible (sewing thread would work well). Try to match the edge of the circle to the string as best as you can: the closer your string matches the circle's circumference, the more accurate your measurement of pi will be. Guide the string around the circle, mark the end of the string, and use the ruler to measure the string's length.
- 2). Measure across the center of the circle with your ruler, from one side to another. This measurement is the circle's diameter.
- 3). Divide Step 1 by Step 2. For example, if your circumference from Step 1 is 44 centimeters, and your diameter is 14 cm, then 44/14=3.14 cm.
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