What size is a giant clam?

The giant clam, Tridacna gigas, or traditionally, pa'ua, is the largest living bivalve mollusc. One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they can weigh more than 227 kilograms (500 pounds) and measure as much as 1.2 metres (4 feet) across, and have an average lifespan in the wild of 100 years or more.[1]