What is the circumference of a 12 foot circle?

The equation for the circumference of a circle is Pi x D (Pi multiplied by the diameter).

So, if you mean the circle has a diameter of 12 feet, then we must multiply 12 by Pi. (Pi is approximately 3.14)

So the circumference is 12 x 3.14 = 37.68 feet, or a bit over 37' 8".