Northern Territory Fisheries legislation prohibits the harvest of Commercially Unsuitable Crabs (CUC’s – those crabs that have recently moulted and have a soft shell) by commercial mud crab fishers. This measure was introduced to reduce the high mortality rate of soft crabs, increase consumer confidence in the product (as soft crabs typically contain little or no meat) and maintain higher prices. Whilst the definition of a CUC is clear, it is qualitative rather than quantitative, a feature of some concern to industry. This work evaluates two commercially available durometers (instruments used to measure the hardness of a range of materials) as a means of quantifying shell hardness in mud crabs. Tests were undertaken on a variety of body parts, with the most useful being the second abdominal plate on the ventral surface for males and the forward quadrants of the carapace for females. Repetitive tests on the second abdominal plate of a male crab led to a 12% decrease in the durometer readings (through softening of the shell), suggesting that only the first few measurements can be used with absolute confidence. Durometer values were independent of both carapace width and wet weight for the range of sizes used.