According to Incubators and hatching Pokémon Eggs:
Each Egg displays the number of kilometers you must walk for the Egg to hatch. In general, the more kilometers required, the rarer the Pokémon that will hatch. A notification will appear when the Egg has hatched.
What are the common distances? I just found my first egg and it requires 5 km to hatch. I'm curious as to how rare that is.
Bonus Questions:
- How rare is it to get an egg from PokéStops?
- What Pokémon can you get from eggs?