An irrational coin - Feeling irrational? It may be a sine to take some deep breaths and trace pi's digits by hand for a calming sensory experience. The number pi (π) is a mathematical constant, approximately equal to 3.14159. It is defined in Euclidean geometry as the ratio of a circle's circumference to its diameter. Included: Pi coin minted in solid copper in West Fork, AR Solid Copper - 29 g 1.54 in (3.9 cm) diameter Antiqued patina This heavy copper coin feels good in the hand and the pocket. The copper coin blank is pre-tumbled before minting for a smooth edge and then given an antiqued finish. Each Pi coin comes in its own wax-sealed packaging with useful and useless pi facts. Engraved by Woody Maringer. Learn more about our artists. Shire Post Mint. All rights reserved.