Flow sensors are essential for a variety of applications in fluidic industries. This paper proposes a liquid flow sensor using a microfluidic channel for macrotubular architectures such as pipes. The sensor comprised a firm poly(methyl methacrylate) microfluidic channel bridge on a mechanically flexible polydimethylsiloxane (PDMS) platform installed on the inner wall of tubular systems. The flexible platform was compatible with various tubular architectures and adopted curvatures. In addition, the microscale fluidic channel surpassed the primary disadvantages of common bulky and rigid flowmeters that cause flow streams disturbance and significant pressure drops in tubular systems. Moreover, the microchannel flow sensor is based on detecting the dominated dynamic pressure generated from the fluid velocity inside the microchannel since the tube flow rate is proportional to the flow velocity inside the channel. The pressure sensors for the microchannel flowmeter displayed a sensitivity of 10 pF/kPa and were fabricated inside the PDMS platform. In particular, the pressure was measured using a capacitive pressure sensor owing to its compatibility with flexible electronics and low power consumption. The capacitive pressure sensor inside the microchannel measure the flowrate based on the force generated on the internal walls from the fluid flow velocity inside the channel. Furthermore, the flow sensor behavior was studied for the overall tubular system and validated using a simulation model for volume flow rate ranging from 500–2000 ml/min.