Approx 1-1/4"x1-1/4", you can make it have a hidden bale see the Accessories section under Omega Enhancers.

Charms and pendants are available in 14kt and 10kt gold, sterling silver and gold plated sterling silver. The precise detail of your favorite team’s logo is captured in expensive metal molds. Items are cast of precious metals and hand finished. All sterling silver pendants are rhodium plated to provide a beautiful lasting finish. The bale on the top of the pendant fits up to a 8mm chain.