Rubber-based diaphragm fibre Bragg grating (FBG) pressure sensor has been widely reported for low pressure sensing with high pressure sensitivity. However, the types of adhesives use and bonding layer thickness always result in large discrepancy between predicted and experimental pressure sensitivity. To investigate this, the pressure sensitivity of the FBG pressure sensor was first calculated using theoretical modelling. The theoretical pressure sensitivity was calculated at 0.5273 nm/kPa. The theoretical modelling was then improved using finite element analysis (FEA). Adhesive strain transfer coefficient was introduced into the theoretical modelling. Experimental pressure sensitivities were obtained to verify the theoretical pressure sensitivity with and without improved method. Experimental pressure sensitivities were obtained to verify the theoretical pressure sensitivity, both with and without the implementation of an improved method. The results revealed a significant discrepancy of more than 78 when comparing the experimental pressure sensitivities with the initially calculated theoretical pressure sensitivity. The introduction of an adhesive strain transfer coefficient has improved the theoretical pressure sensitivity reducing the discrepancy to within 10. In addition, the results demonstrated that cyanoacrylate adhesive with minimal possible thickness is the best option for achieving the highest achievable pressure sensitivity. © 2024 Elsevier Ltd