How many Earth-like planets are there?
The Drake equation (please look it up) estimates about 50,000 in our galaxy, the Milky way. However, they are many light years away and there is little chance of ever contacting them, (that is, postulating Special Relativity) and so there may as well be none.
Even a Starship, which may travel the speed of light, would not be fast enough. Apart from Special Relativity forbidding massive objects attaining the speed of light, the problem of the ship hitting space dust or larger objects in space at that speed would have to be overcome with a massive barrier shield in front of the spaceship. This is all science fiction, however. The technology just does not exist and there is little on the horizon to indicate that it will ever exist.
Really we are effectively alone in the universe.
It depends on what you mean by earth like.
To explain if you mean terrestrial and within the habitable zone of its star then it is estimated that there is roughly one such planet per star in our galaxy. (This is rough becasue of our limited knowledge and the variability of formation of things we literally cannot see) with 400 billion stars in the milky way you get 400 billion. If you wish to speculate on outside of a milky way then we have assumption but no data so it's pure speculation. Effectively the number is infinity for human purposes.
If you mean more earth like than that it depends on how "earth like" you mean and what parameters to follow. Nitrogen predominant atmosphere? Oceans? Carbon based life? 4 billion years old? The numbers would get smaller and smaller yet since the sample size is so big we get a grand total of we have no idea.
Hope this helped.
As an exercise, I did the following calculation. Take it as you wish.
This percentage of
0.1% have planets. Of those,
0.1% Are the correct distance. Of those
0.1% Planet has the conditions. Of those
0.1% Have life. Of those
0.1% Is advanced as ours, or more
10^-9 Total factor
Given there are:
100 Billion stars per Galaxy
200 Billion known Galaxies
This gives 20 million planets in the Universe with life as advanced as ours.
To account for only one in our Galaxy, all those 0.1% factors change 0.63%. This makes one such planet per galaxy, or 100 billion.
Just for laughs...
Unknown. We do know that at least 70% of solar systems are radically different from our own.
We don't yet know how many solar systems are like ours - maybe very few.
We don't yet know whether Earth-like planets can still exist in most of the unfamiliar solar systems. As the moon of a Hot Jupiter, for instance. Nor whether rocky planets larger than the Earth but a suitable distance from their star would be Earth-like. An exoplanet similar to Venus might look promising, for instance.
Best guess: more than ten.
Considering the Universe looks to be infinite - it may not be possible to give a single number answer.
If you want to know how many have been confirmed... that would be 10 last I looked. There may be a few more in the literature that have not made mainstream yet. By the time I found them, there'd probably be a few more. It'll be a moving target for a while yet.