This is by no means the official answer.
It will take some testing on the part of the game creator to figure this out. I have made games on my work computer which played fine, only to take them home and find that they lagged a little more than I would like.
A good starting point may be the specs on the system you use to create the game, but if your specs are high, you will cut out some of the market. If it is a relatively simple game, with a minimum of entities and enemies, you can lower the specs from there, but it will take some testing.
Also, there is a distinction between minimum specs and recommended specs. It's a good idea to make your recommended specs a little higher than they need to be.
Crazy Grandpa