there are 40B earth-like planets in the habitable zone in the galaxy.

2014-12-05:

the number of biotic planets in the Milky Way is between millions and billions, and the corresponding distance to the nearest biotic world is 10-100 light years. the likely distance to the nearest civilizations detectable by SETI is of the order of a few 1000 light years

this is a very accessible paper on the Drake equation (which may well achieve a cultural status similar to e=mc^2 this century)

1% of the stars in the Milky Way could have earth like planets (smaller rock like planets) Another study shows the Milky Way is twice as big as previously thought. So instead 100b stars there could be 200b and of those 1% or 2b could have earth like worlds around sun like stars.