## Step 2: Diameter

Where C is circumference and D is diameter. You can test this formula at home with a round dinner plate. If you measure the circumference and the diameter of the plate and then divide C by D, your quotient should come close to Pi . Another way to write this formula is: C = Pi * D where * means multiply. This second formula is commonly used in problems where the diameter is given and the circumference is not known (see the examples below).