The best estimate is that the observable universe contains around one septillion stars. That’s a 1 followed by 24 zeros: 1,000,000,000,000,000,000,000,000. To put that in plain terms, there are almost certainly more stars in the universe than there are grains of sand on every beach and in every desert on Earth, combined.
And here’s the honest catch that makes the number even more astonishing: nobody counted them. That figure is a careful estimate, built up from what we can see and extended out to what we can’t. So let’s unpack where such a staggering number comes from, and why it’s still only an educated guess.
The Short Answer: About a Septillion
When astronomers tally it all up, the number they most often land on is roughly 10^24 stars, or one septillion. Some estimates run a bit lower, in the range of a couple hundred sextillion (that’s 2 followed by 23 zeros), and it may well climb higher as our telescopes find more faint galaxies. But “about a septillion” is the figure you’ll see quoted most, including by NASA.
It’s a number so far outside daily experience that it stops meaning anything. You simply cannot picture a septillion of something. Which is exactly why scientists reach for a comparison that hits home.
More Stars Than Grains of Sand
The famous line, often credited to astronomer Carl Sagan, is that there are more stars in the universe than grains of sand on all the beaches of Earth. It sounds like poetry, but the math actually backs it up.
If you estimate the size of every grain of sand and the volume of every beach and desert on the planet, you land at roughly 7.5 quintillion grains, that’s a 7 followed by 18 zeros. That’s a mind-bending number in its own right. Yet the stars still win, and they win big, outnumbering every grain of sand on Earth by a factor of at least a thousand. When you’re outside on a beach, remember that the entire shoreline beneath your feet couldn’t match the stars overhead.
How Do You Count the Uncountable?
Obviously, no one is out there ticking off stars one by one. So how do astronomers arrive at a septillion?
They do it with clever extrapolation. First, they estimate how many stars live in a typical galaxy. Our own Milky Way holds somewhere between 100 and 400 billion, and you can get a feel for that scale in our piece on how many solar systems are in the Milky Way. Then they estimate how many galaxies fill the observable universe, a number thought to run from 100 billion to as many as 2 trillion. Multiply the two together, and you arrive at that eye-watering septillion.
Deep-field images like the one above are the key. By pointing a telescope at a tiny, seemingly empty patch of sky for hours and counting the thousands of galaxies that appear, astronomers can work out how densely galaxies are packed and scale that up across the entire sky. It’s less like counting and more like careful, cosmic sampling. And it’s worth remembering how little of this we ever see directly: on a clear, dark night, the human eye can make out only about 5,000 stars.
Why It’s Still Only an Estimate
Two things keep this number fuzzy, and both are fascinating.
The first is that we can only count what’s inside the observable universe, the bubble of space whose light has had time to reach us since the Big Bang. Beyond that edge, the universe almost certainly continues, and it may even be infinite. If it is, then the true number of stars isn’t just unknown, it’s endless. Our guide to how vast the universe really is explores that dizzying idea.
The second is that most stars are faint. The most common stars in the cosmos are small, dim red dwarfs, far too feeble to spot across intergalactic distances, so our counts almost certainly miss enormous numbers of them. If anything, a septillion is probably a conservative estimate. You can keep exploring the science on NASA’s overview of stars.
So the next time you look up, hold this thought: every star you can see, plus every one you can’t, across every galaxy in every direction, adds up to a number so vast that a beach full of sand is a rounding error. That’s the universe we live in.
If you enjoyed this article, don’t forget to drop us a comment, it really helps support the site, and be sure to check out our other articles because we think you’re going to love them too.