# Calculate the Circumference of a Circle

Whether you're doing craft work, putting fencing around your hot tub, or just solving a math problem for school, knowing how to find the circumference of a circle will come in handy in a variety of circle-related problems.

## Steps

### Circumference Help

Doc:Circumference of a Circle Diagram,Circumference of a Circle Calculator

### Using the Diameter

1. Write down 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 to say, you can find the circumference of a circle just by multiplying the diameter by pi. Plugging π into your calculator will give you its numerical value, which is a closer approximation of 3.14.
2. Plug the given value of the diameter into the formula and solve.
• Example problem: You have a circle tub with a diameter of 8 feet, and you want to build a white fence that creates a 6-foot wide space around the tub. To find the circumference of the fence that has to be created, you should first find the diameter of the tub and the fence which will be 8 feet + 6 feet + 6 feet, which will account for the entire diameter of the tub and fence. The diameter is 8 + 6 + 6, or 20 feet. Now plug it into the formula, plug π into your calculator for its numerical value, and solve for the circumference:
• C = πd
• C = π x 20
• C = 62.8 feet

1. Write down the formula for finding the circumference of a circle using the radius. The radius is half as long as the diameter, so the diameter can be thought of as 2r. Keeping this in mind, you can write down the formula for finding the circumference of a circle given the radius: C = 2πr. In this formula, "r" represents the radius of the circle. Again, you can plug π into your calculator to get its numeral value, which is a closer approximation of 3.14.
2. Plug the given radius into the equation and solve. For this example, let's say you're cutting out a decorative strip of paper to wrap around the edge of a pie you've just made. The radius of the pie is {{safesubst:#invoke:convert|convert}}. To find the circumference that you need, just plug the radius into the equation:
• C = 2πr
• C = 2π x 5
• C = 10π
• C = {{safesubst:#invoke:convert|convert}}.

## Tips

• Consider buying an advanced calculator that already has π as one of the buttons. This will mean less typing for you and a more accurate answer because the π button produces an approximation to π that is much more accurate than 3.14.
• To find circumference from diameter, just multiply pi by the diameter.
• Remember: some worksheets will ask to replace pi with a subside, such as 3.14 or 22/7.
• Radius is always going to be half diameter..

## Warnings

• Remember to always double-check your work because one mistake will set off all your data.
• If you are stuck, ask a friend, family member, or teacher. They will always help!