An interferometric Fabry-Pérot cavity based on hollow-core ring photonic crystal fiber (HCR-PCF) for pressure sensing is proposed. The sensing head is formed by splicing a small section of HCR-PCF to standard single mode fiber. The spectral response depends on the cavity length due to the geometry of the HCR-PCF. The sensing head is subjected to methane pressure variations, where it exhibits a sensitivity of 0.82 nm/MPa. Its response to nitrogen pressure variation is also studied. Besides, the sensing head intrinsic sensitivity to the nitrogen refractive index variations inside the hollow-core was estimated. Finally, temperature measurement is performed and a sensitivity of 3.77 pm/ºC is obtained for temperatures below 200 ºC.