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.
- How rare is it to get an egg from PokéStops?
- What Pokémon can you get from eggs?
Eggs come in three distances: 2km (1.2mi), 5km (3.1mi), and 10km (6.2mi). The distribution of these seems to be relatively random, however 5km seems to be somewhat more common than the others. 10km seems to be somewhat rarer for now, however these numbers have become extremely balanced since the beta.
Pokemon’s strength (and rarity) is usually determined by the distance you need to walk to hatch the Egg.
You can get any non-legendary (and egg-grouped Pokemon) from eggs, although some are rarer than others. For instance, you’re much more likely to get a Rattata than a Growlithe from an egg.