Abstract <p>This paper presents an ultrasonic-guided wave technique for measuring the fluid level using a helical waveguide sensor. The torsional T(0, 1), longitudinal L(0, 1), and flexural F(1, 1) modes were propagated concurrently in the waveguide (WG) utilizing through-transmission (TT) and pulse-echo (PE) approaches. We used a stainless-steel wire to make the helical sensor, and both dead ends of the sensor were connected to the shear transducer at 45° orientations to transmit and receive all three modes using TT and PE techniques simultaneously. Experiments were performed with various fluids (glycerin, water, and petrol) to determine the level (0.5 to 100 mm). The amplitude of all three modes decreased because of wave leakage when the sensor portion (helical) was inside the liquid medium. The fluid level was measured based on the sensor’s reflection factor due to the amplitude drop of each wave mode. Multiple experiments (T1, T2, T3) were performed to ensure the sensor’s repeatability. Also, the micro-fluid level was measured at every 0.5 mm depth increment using Fast Fourier Transform (FFT) of F(1, 1) mode using PE and TT concepts. Finally, the F(1, 1) mode provides better level sensitivity than other wave modes. This technique can especially be used in hazardous or inaccessible regions of interest to simultaneously monitor fluid levels and temperature in oil industries and nuclear power plants.</p>