A good ability to hear is one of the important senses of a human being. Loss of hearing has various effects to the life of a person. A hearing-impaired person will have less social communication, fewer educational and job opportunities. Also, he faces emotive problems caused by a reduction in self-confidence. So, a need of designing an optimal hearing aid is very much necessary to solve the problem of hearing loss. In this paper a design of optimal ten sub band Finite Impulse Response filter bank is designed for the hearing aid. Hamming window is preferred to design the FIR filter than other windowing techniques owing to its relatively sharp main lobe width and also the first few lobes have good attenuation. The filter bank is designed with variable bandwidths by changing the center frequency and bandwidth. So instead of using a fixed bandwidth design, the filter bank bandwidths can be altered according to the audiogram of hearing-impaired person. This leads to design of a highly qualitative design compared to fixed bandwidth designs with high audiogram matching and less matching error.