Charmander eggs take 5,355 steps to hatch in all Pokémon games after Generation I. This total comes from a base 21 egg cycles needed to hatch the egg, with each egg cycle consisting of 255 steps.
You can speed up the hatching process if you have a Pokémon with the move Flame Body or Magma Armor in your party with the egg. Having a Pokémon with these moves in your party counts each egg cycle twice, halving the steps needed to hatch the egg. The message displayed by the egg also gives you an indication of how close it is to hatching.