The Amoghasiddhi Buddha amulet itself is approx.  1.75" in diameter.  The overall length of the Feng Shui Amoghasiddhi Buddha Keychain Amulet is approx. 4.5".  It is made of metal.

Warning: This product can expose you to chemicals, which are known to the State of California to cause cancer, birth defects or other reproductive harm. Details go to www.p65warnings.ca.gov .