The blue swimming crab (Portunus pelagicus) is an important commercial species in Phuket Province, Thailand but it is difficult to handle these spiny crabs to measure their carapace length and width directly. On the other hand it is easy to measure their weight only as much handling is not needed in this case. The aim of this study was to make correlations between body wet weight and carapace length, as well as body wet weight and carapace width of blue swimming crabs from Andaman Sea, Phuket Province.