· just now. 1  Pi Measurement. 2  The value of pi is the ratio of the circumference of a circle to its diameter. 3  For the best answers, search on this site https://shorturl.im/avMXc. 4  Pi is the ratio of a circle's circumference to its diameter. No matter how big or small a circle is, if it's a perfect circle, then the distance around is a little more than 3 times the distance across the middle of the circle. More info here: http://en.wikipedia.org/wiki/Pi.