Electromagnetic waves transport momentum while traveling through space. The corresponding momentum density is expressed in terms of the Poynting vector magnitude and the speed of light. By substituting the volume occupied by the wave that passes through an area in a short interval of time, the momentum flow rate per unit area can be obtained. The average rate of momentum transfer per unit area is obtained by replacing the average value of the Poynting vector with intensity. Due to the transfer of momentum, electromagnetic waves exert pressure on the surface, known as radiation pressure. Now, the average rate of change of momentum equals average force and force per unit area is the radiation pressure. Thus, the radiation pressure is directly proportional to the intensity of the wave. If the surface perfectly absorbs the electromagnetic wave, the corresponding momentum is also transferred completely to the surface. For a perfectly reflecting surface, the momentum change will be double. Thus, the radiation pressure also doubles.