For over 20 years, the Pokémon series has, through seven generations, introduced us to hundreds of different Pokémon. 806, to be exact. Despite striking similarities between certain designs, from Bulbasaur at No. 1 to Blacephalon at No. 806, every single creature is still unique in their own way. This can come in many forms, be it appearance, individual ability, or even shape and size.
Listed in the Pokédex at just 4" tall, Joltik, Flabébé, Cutiefly, Comfey, and Cosmoem are the shortest known Pokémon, while at an incredible 47'7", Wailord is the largest of all so far.
Yet, due to the limitations of handheld gaming devices, throughout every game in every region, all Pokémon have had the same screen space in which to fit. This makes it difficult for the games to convey the difference in size between the creatures.
In some circumstances, we are shown the size of certain Pokémon outside the constraints of battle. This usually happens just before encountering Legendary Pokémon, meaning we have some idea of the size of the likes of, among others, Groudon, Giratina, and Reshiram.
It is the more common Pokémon that are harder to tell apart in terms of size, and it's not until you look in your Pokédex that you realise just how big some of these monsters actually are.