The accurate determination of the transfer function of ultrasound transducers is important for their design and operational performance. However, conventional methods for quantifying the transfer function, such as hydrophone measurements, radiation force balance, and pulse-echo measurements, are costly and complex due to specialized equipment required. In this study, we introduce a novel approach to estimate the transfer function of ultrasound transducers by measuring the acoustic streaming velocity generated by the transducer. We utilize an experimental setup consisting of a water tank with a millimeter scale, an ink-filled syringe, and a camera for recording the streaming phenomenon. Through streaming velocity measurements in the frequency range from 2 to 8 MHz, we determined the transfer function of an unfocused circular transducer with a center frequency of 5 MHz and a radius of 5.6 mm. We compared the performance of our method with hydrophone and pulse-echo measurements. At the center frequency, we measured a transmit efficiency of 1.9 kPa/V using the streaming approach, while hydrophone and pulse-echo measurements yielded transmit efficiencies of 2.1 kPa/V and 1.8 kPa/V, respectively. These findings demonstrate that the proposed method for estimating the transfer function of ultrasound transducers achieves a sufficient level of accuracy comparable to pulse-echo and hydrophone measurements.