In this paper, we design and analyze flexible wireless power transfer (WPT) coils for flexible wearable devices. The 3 cm by 3 cm flexible coils are designed using polyimide substrate. The coil is designed as thin as possible to achieve higher Q-factor and power transfer efficiency (PTE). Furthermore, we analyzed the mutual inductance between the coils with a bending radius of a receiver (Rx) coil of infinite, 26 mm and 13 mm by considering the curvature of the human wrist. As the results, the simulation results of the flexible coil are verified with the measurement results using Z-parameter analysis in the frequency range from 1 MHz to 50 MHz. In conclusion, we verify the mutual inductance simulation results with the measurement results within the average error of 2.85%.