The most cited global estimate puts the number of trees on Earth at about three trillion. NASA gives the Milky Way somewhere between 100 and 400 billion stars. Three trillion is more than seven times the high end of that range, so there are indeed more trees on Earth than stars in our galaxy.
Both numbers are more interesting than the comparison that pairs them, partly because neither is a count.
Where the tree number comes from
The three trillion figure is modern, and it changed the way people talked about global tree numbers. It comes from a study led by Thomas Crowther, published in Nature in 2015, which put the global total at about 3.04 trillion.
The striking part is what it replaced. The previous commonly repeated estimate was in the hundreds of billions, built from satellite imagery and forest-area calculations alone. The 2015 study added more than 400,000 ground-based tree-density measurements to the satellite picture and arrived at a number roughly an order of magnitude higher. The trees did not appear between the two studies. The method improved. A count built only from above had been undershooting what was actually on the ground.
So the headline number is best read as a careful estimate from a particular study, not a tally. It is the most thorough attempt so far, not a final figure, and it carries its own uncertainty.
Why the star number is a range, not a figure
The star count is uncertain for a different reason, and the gap between 100 and 400 billion is not sloppiness. It reflects something real about how the number is reached.
Nobody counts the stars in the Milky Way one by one. Dust blocks much of the galaxy from view, and most of it lies too far away to resolve into individual stars. Instead astronomers estimate the galaxy’s mass, work out how much of that mass is in stars, and divide by the mass of an average star. That last step is where the range opens up. The most common stars by far are faint, low-mass red dwarfs, which give off very little light and are easy to undercount. A small uncertainty in how many of those there are turns into a large uncertainty in the total. The European Space Agency’s Gaia mission has mapped the positions of well over a billion stars, but even Gaia cannot see the faintest of them, so the galaxy-wide figure stays a range.
One number rests on filling the gaps in satellite data with ground samples. The other rests on dividing a mass estimate by an average. Neither is a head count, and both have honest error bars.
The comparison only works at galaxy scale
The factoid is careful to say stars in the Milky Way, and that limit is doing the heavy lifting.
Earth has more trees than our galaxy has stars. It does not have more trees than the universe has stars, and the gap there is not close. A Hubble-based estimate discussed by NASA suggested the observable universe could contain about two trillion galaxies, and NASA estimates the universe could hold up to a septillion stars, a one followed by twenty-four zeros. Against that, three trillion trees is a rounding error.
So the comparison is true and also narrow. Pick our galaxy and the trees win. Widen the frame to the observable universe and the stars outnumber every tree that has ever grown on Earth by something like twelve orders of magnitude.
The part of the tree number worth keeping
There is a figure in the same study that tends to get dropped when the factoid is repeated, and it is the one that matters most.
The Crowther study also estimated that the number of trees on Earth has fallen by about 46 per cent since the start of human civilisation, and that more than 15 billion trees are lost each year. The three trillion that remain are roughly half of what once stood. The cheerful version of the factoid, that trees outnumber the stars in the galaxy, sits on top of a second finding that is harder to enjoy.
What to keep from the factoid
The comparison is sound. There are more trees on Earth, about three trillion by the best current estimate, than there are stars in the Milky Way, somewhere between 100 and 400 billion.
Both numbers are estimates rather than counts, reached by different methods with real uncertainty, and the comparison holds only because it stops at the edge of our own galaxy. The more durable fact underneath it is that the three trillion is a reduced number. The same study estimated that Earth has lost about 46 per cent of its trees since the start of human civilisation, and that more than 15 billion are cut down each year.
