Radiation pressure is the pressure associated with the interaction of electromagnetic radiation on any given surface. In other words Radiation pressure is defined as force per unit area exerted by electromagnetic waves.
Mathematically,
Radiation Pressure = Force / Area = Intensity of wave (I) / Speed of light(c) .
Dimensional Formula of Intensity of wave = M1L0T-3
Dimensional Formula of Speed of light = M0L1T-1
Putting these values in the given equation we get,
Dimensional Formula of Radiation pressure = M1L-1T-2
SI Unit of Radiation pressure is N/m2 (newton per square meter)