This study presents the dependence of strain sensitivity on cavity length in conventional Fabry–Perot (F‐P) sensors. A high number of F‐P sensors were required and to ensure their reproducibility, a manufacturing process was developed to obtain similar sensors but with different types of lengths. A hollow‐core silica tube was used to fabricate several F‐P cavities by fusion splicing it between two sections of SMF28 fiber. The fabricated F‐P has a varying length ranging from 15 to 2500 μm. The cavities were measured under a microscope and the reflected spectrum was acquired for each one. Strain measurements were performed for a maximum strain of 1000 με. The strain sensitivity showed a highly linear correlation with ∆λFSR. Small length variations for short cavities heavily affect the FSR value. The smallest and longest cavities present sensitivities of 8.71 and 2.68 pm/με, respectively. Thermal characterization for low‐ and high‐temperature regimes was also performed and is constant for tested sensors.