Whether you're doing handwork, putting fences around a hot tub, or simply solving a math problem for school, knowing how to figure out the circumference of a circle will come in handy for a variety of circle-related problems. If you want to know how to calculate the circumference of a circle, just follow these steps.
Method 1 of 2: Using Diameter
Step 1. Write the formula for finding the circumference of a circle using the diameter
The formula is simply this: C = πd. In this equation, "c" represents the circumference of the circle and "d" represents its diameter. That is, you can find the circumference of a circle just by multiplying the diameter by pi. Putting π on your calculator will give you its numerical value, which is an approximation of 3, 14.
Step 2. Put the diameter into the equation and solve
- Example: let's say you are solving this problem. You have a round spa bath with a diameter of 3 meters and you want to build a fence that creates a space of 2 meters around the bathtub. To find the circumference of the fence that needs to be created, you must first find the diameter of the bathtub and the fence, which will be 3 meters + 2 meters + 2 meters, which will add up the entire diameter of the bathtub and the fence. The diameter is 3 + 2 + 2, or 7 meters. Now, put that value into the formula, put π on the calculator to get its numeric value, and solve for the circle:
- C = πd.
- C = π x 7.
- C = 21.9 meters.
Method 2 of 2: Using Lightning
Step 1. Write the formula for finding the circumference of a circle using the radius
The radius is half the length of the diameter, so the diameter can be thought of as 2π. With that in mind, you can write the formula to find the circumference of a given radius: C =. In this formula, "r" represents the radius of the circle. Again, you can put π into your calculator to get the result of its numerical value (3, 14).
Step 2. Put the radius into the equation and solve
For this example, let's say you're cutting a strip of decorative paper to tie around a pie you just made. The pie radius is 5 cm. To find the circumference you need, just put the radius in the equation:
- C = 2πr.
- C = 2π x 5.
- C = 10π.
- C = 31.4 cm.
- Buy a scientific calculator that already has π as one of the buttons. This will mean less stuff to type and a more accurate answer, as the π button gives an approximation of π that is much more accurate than 3, 14.
- To find the circumference from the diameter, multiply pi by the diameter.
- The radius value will always be half the diameter.
- Some problems will require you to replace pi with an approximate value such as 3, 14 or 22/7
- Remember to always check your work more than once: a simple mistake will rebound on all your data.
- Take it easy. Remember the old saying: better safe than sorry.
- If you are stuck, ask a friend, family member, or teacher for help. They will always help you!