Let us assume the pizza to be a circle.
Then the radius of the circle is, D = 12 in.
Therefore, the radius of the circle is,
[tex]r=\frac{D}{2}=\frac{12in}{2}=6in[/tex]Now, the circumference of the circle can be calculated as,
[tex]C=2\times\pi\times r=2\times3.14\times6in=37.68in[/tex]Thus, the circumeference is 37.68 in.