1) The number of galaxies. Some 100 billion galaxies are visible to modern telescopes and the total number in the universe is believed to exceed this number, but we will be conservative.
that's 100,000,000,000.
2) The number of stars in an average galaxy. As many as hundreds of billions. Lets call it just 100 billion.
that's 100,000,000,000.
The number of stars in the universe.
So the total number of stars in the universe is roughly 100 billion x 100 billion.
that's 10,000,000,000,000,000,000,000 stars, 10 thousand, billion, billion. And thats a conservative estimate.
3) The number of stars that have planetary systems. So far only around 50 have been discovered so we have very little data to work on for this estimate. Current technology dictates that a star needs to be to close to us for a planet to be detected, usually by the stars 'wobble'. Even so most cosmologists believe that planetary formation around a star is quite common place. For the sake of argument let us say it is not and rate it at only one in a million and only one planet in each system, as we want a conservative estimate, not an exaggerated one. That calculation results in
10,000,000,000,000,000 planets in the universe. Ten million, billion
4) The number of Earth like planets. Let's assume that this is very rare among planets. Only 1 in a million, and this is also being very conservative in as much that we are assuming here that only Earth like planets are suitable for the formation of life. Simple division results in:
10,000,000,000 planets in the universe capable of producing life. Ten billion.