[header] How to calculate the circumference of a circle [title] Write down the formula for finding the circumference of a circle using the diameter. [step] The formula is simply this :. 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 or 22/7.