Abstract: A compact air pressure gauge assembly mountable to the valve stem of a inflatable tire or mountable through the rim of a wheel for continuous monitoring of the tire inflation pressure. The air pressure gauge assembly has a compact design to extend the valve stem or wheel rim relatively little to avoid curb contact and interference with the wheel balance. By positioning the air intake in a right angle with the opening for receiving a standard valve stem or by positioning the air intake straight across the opening for receiving the valve stem while the dial face is positioned in an right angle, the air intake is separated from the airtight chamber housing the sensing element. A diaphragm having a simple mechanical design is provided as sensing element. The diaphragm includes a membrane being connected with a pressure indicator that moves up and down according to the tire pressure.