Pokémon Black Version and Pokémon White Version - Weight
Weight is specified in tenths of a kilogram. The weight is modified by applying the weight reductions from Autotomize, then all other weight modifications. Such other effects are combined in a single multiplier. The weight is multiplied by this multiplier and rounded half-down to the nearest tenth of a kilogram to get the Pokémon’s current weight. However, the weight can’t be less than 0.1 kg. A Pokémon’s weight starts as its weight for the Pokémon’s species when it enters the battle, and it reverts to that value when the Pokémon leaves the battle.