Shell resource utilization in two common species of hermit crabs, Calcinus latens (Randall) and Calcinus gaimardii (H. Milne Edwards), from intertidal and subtidal zones at Kenting, southern Taiwan, was studied. Field data were compared with laboratory results in shell-selection tests. Shell parameters examined included shell length, shell width, aperture length, aperture width, and weight in sea water. Crab parameters examined included carapace length, shield length, and wet weight. Most intertidal C. latens did not use the most abundant shell type in the field, but showed a strong preference for the most abundant shell type in shell-selection tests. The small size of the most abundant shell type in the field appeared to be responsible for this pattern. The results of shell-fit tests showed that most crabs lived in adequate shells at least in terms of internal volume. Shell-selection tests, however, proved that larger crabs (carapace length > 5 mm) are more shell-limited than smaller ones by SAI (shell adequacy index) values. Larger crabs would select much larger shells if they were available. Differences in shell utilization between the subtidal C. latens and C. gaimardii are discussed.