Stock assessments using acoustic surveys face the challenge of improving measurement accuracy due to several bias factors such as high species diversity, body shape, and size. The target strength (TS) value reflects the object size (Total length (TL)). The size value was used to convert the weight of the object. Stock assessment of an object was obtained by multiplying the abundance of the object by its weight. TS measurements were performed on the individual of each species object and various sizes. Numerical data analysis using the best-fit linear regression technique was used to determine the relationship between total length and TS. There has been no research undertaken on the TS of Puerulus.  The ex situ target strength of two Puerulus species, the scalloped spiny lobster (Panulirus homarus) and the ornate spiny lobster (Panulirus ornatus), has been successfully measured. The results indicated that the fit length-TS relationship for the scalloped spiny lobster with a total length (TL) of 18-21mm was TS_200kHz = -137.595 + 61.75log₁₀ (TL) (R² = 0.98) and for the ornate spiny lobster was TS_200kHz = -104.96 + 36.54log₁₀ (TL) (R² = 0.95). The use of the Stochastic Distorted Wave Born Approximation (SDWBA) Model to see the backscatter value on each body part shows that the straight body shape has a different backscatter value, especially on the cephalothorax. A comparison was made of the measured TS values in situ with the SDWBA model in the frequency range 160-240 kHz against the total length at the same frequency of 200 kHz. The results obtained from this comparison show almost the same TS value against the total length. These validated that the TS-length relationships can reduce bias in acoustic measurements by providing improved modeled TS estimates for the spiny lobster puerulus.