A tire pressure gauge apparatus for securing to a vehicle tire valve stem mounted to a tire valve stem port in a vehicle tire, the valve stem including a tubular stem body containing a valve assembly having a valve opening mechanism, the stem body having a stem connection end fitting sealingly to the tire valve stem port, and having a stem air receiving end, the apparatus including a housing for placement in fluid communication with received air from within the tire; a structure for opening the valve opening mechanism; and a pressure equilibration structure dividing the housing into a received air chamber and a biasing gas chamber and including a pressure indicator element, the pressure equilibration structure and the pressure indicator element being movable relative to the housing, and the pressure indicator element displaying a pressure reading of received air from within the tire which varies with the position of the pressure equilibration structure relative to the housing; so that alteration of the pressure of received air within the received air chamber from the valve stem causes movement of the equilibration structure within the housing to re-establish pressure equilibrium between biasing gas sealed within the biasing gas chamber and received air within the received air chamber, and movement of the equilibration structure causes the indicator element to move relative to the housing to provide a received air pressure reading.