Energy band nonparabolicity is present in the materials such as graphene, GaAs, HgCdTe, InSb, wurtzite GaN etc. The energy levels for the nonparabolic subbands are different fromparabolic subbands. In this work we discuss about nonparabolicity factor and find its numerical value in monolayer, bilayer and multilayer graphene. We also discuss how the nonparabolicity affects the density of states of graphene. The density of states function tells us how many quantum states are available in the band per unit energy level. The nonparabolic effects are more pronounced in two-dimensional system because carriers in subbands are always away from the band edge. Here, we use a dispersion relation that can be used to describe nonparabolicity in a variety of materials and device structures. This dispersion relation is based on KaneÂs k.p model and is suitable for both narrow and widegap nonparabolic materials.