Disclosed is a device and method for measuring pressure inside a deformable vessel containing a compressible gas, by the transfer of pressure inside the vessel to a primarily rigid chamber external to the vessel through a flexible membrane covering a window in the chamber, which is filled with a suitable incompressible fluid. The pressure transfer is effectuated by either pressing the vessel against the chamber or the reverse. The transferred pressure is then measured by a traditional gauge or other available pressure sensor. Depending on the elasticity of the vessel exterior wall, a fixed area for compressing a flat area of the vessel exterior wall and transfer membrane is chosen. At this chosen amount of deformation, the pressure differential between the vessel interior and the exterior chamber is zero, facilitating the external measurement of the vessel internal gas pressure.
