# How many grains of sand are on earth’s beaches?

Here's an old, old, question, but this time with a surprise twist. The question is — and I bet you asked it when you were 8 years old and sitting on a beach: Which are there more of — grains of sand on the Earth or stars in the sky?

Obviously, grains and stars can't be counted, not literally. But you can guestimate.

Science writer David Blatner, in his new book Spectrums, says a group of researchers at the University of Hawaii, being well-versed in all things beachy, tried to calculate the number of grains of sand.

They said, if you assume a grain of sand has an average size and you calculate how many grains are in a teaspoon and then multiply by all the beaches and deserts in the world, the Earth has roughly (and we're speaking very roughly here) 7.5 x 1018 grains of sand, or seven quintillion, five hundred quadrillion grains.

That's a lot of grains.

OK, so how about stars? Well, to my amazement, it turns out that when you look up, even on a clear and starry night, you won't see very many stars. Blatner says the number is a low, low “several thousand,” which gives the sand grain folks a landslide victory. But we're not limiting ourselves to what an ordinary stargazer can see.

Our stargazer gets a Hubble telescope and a calculator, so now we can count distant galaxies, faint stars, red dwarfs, everything we've ever recorded in the sky, and boom! Now the population of stars jumps enormously, to 70 thousand million, million, million stars in the observable universe (a 2003 estimate), so that we've got multiple stars for every grain of sand — which means, sorry, grains, you are nowhere near as numerous as the stars.

So that makes stars the champions of numerosity, no?

Ummm, no. This is when Blatner hits us with his sucker punch. Yes, he says, the number of stars in the heavens is “an unbelievably large number,” but then, very matter-of-factly, he adds that you will find the same number of molecules “in just ten drops of water.”

Say what?

Let me repeat: If you took 10 drops of water (not extra-big drops, just regular drops, I'm presuming) and counted the number of H2O molecules in those drops, you'd get a number equal to all the stars in the universe.

This is amazing to me. For some reason, when someone says million, billion or trillion, I see an enormous pile of something, a grand scene, great sweeps of desert sand, twirling masses of stars. Big things come from lots of stuff; little things from less stuff. That seems intuitive.

## Stars or Sand? Are there more Grains of Beach Sand or Stars in our Visible Universe?

This began as a simple question, but it has intrigued enough people that I decided to feature it as an article and expand it so we can have some fun.

_____________Carol Charming:

“I have heard people say that there are more stars in the universe than there are the grains of sand ‘on the beach.’

What size is the beach and are the grains of sand coarse or fine? Or does the saying go “all the grains of sand on all the world’s beaches,” something I simply can’t believe to be true.”

Carmel (Charmel) Beach has many more grains of sand than our Milky Way has Stars

• Disclaimer —
You and I will work through to get an answer, but be warned — There will never be a definitive, conclusive, absolute, precise or final answer to this question.
• For either counting stars or sand grains — there simply is no measurement, or accurate calculation or mathematical proof or method of counting – nor will one ever conceivably exist.
• Its even worse than that — we can’t even get approximate numbers with much confidence.

We can only roughly estimate the number of stars in our own galaxy. Estimates easily vary by 150 times (more than two orders of magnitude) and estimates of the number of grains of beach sand are even worse.

So if we can credibly estimate either the number of stars or sand grains within say four or five orders of magnitude of the other estimate – we’ll be doing well.

However, as mentioned above, this essentially guarantees that answers to this question will be off by a few magnitudes; or they will have, in more diplomatic terms, “a high variance” or “a large margin of error.”

Even using the best available evidence and methods – no one can credibly claim their answers to either estimate of stars or sand grains are within 20 percent (and 20 percent of a trillion stars / sand grains is an error of 200 billion.

That’s more than ten magnitudes larger than a measuring error of one star or one grain of sand). And that’s my estimate on the best numbers we can ever do.

What we can do instead is try to use reasonable methods, use the broadest range of assumptions (lowest and highest) and use the most credible methods available to get estimates for both sand grains and for star counts.

Then, after we have estimates (with each having its own range of variance) the only way I can reasonably imagine deciding there are more stars than sand, or more sand than stars, is if one estimate comfortably exceeds the other by six or more magnitudes; a million times larger or smaller.

* And so, because of the gigantic estimation errors inherent in this exercise – you might take a big breath (now let it out) and try to keep a sense of humor in mind while reading this.

With that disclaimer in mind, shall we start ?

1. Stars: We are going to multiply estimates of stars in our galaxy with an estimate of the number of galaxies — even though the number of stars in a galaxy can vary by more than five magnitudes; from 10 million to a trillion stars (and we really don’t have a good grasp on how many galaxies there are.)

## Are there more stars in the universe than grains of sand on Earth?

Are there really more stars in our universe than there are grains of sand on all the beaches on Earth?

Are there really more stars in our universe than there are grains of sand on all the beaches on Earth?

It may hurt your brain to think about it, but it seems that the answer is likely to be yes, or at least the numbers are roughly in the same ballpark.

Astronomers actually set out to answer this question about a decade ago. It's a tricky problem to solve, but it's slightly easier if you throw in a couple of qualifiers — that we're talking about stars in the observable universe; and grains of sand on the entire planet, not just the beaches.

The scientists started by measuring the luminosity density of a section of the universe — this is a measurement of how much light is in that space.

They then used this measurement to estimate the number of stars required to create that amount of light. This was quite a mathematical challenge!

• “You have to assume that you can have one type of star represent all types of stars,” says astronomer Simon Driver, Professor at the International Centre for Radio Astronomy Research in Western Australia and one of the scientists who worked on the question.
• “Then let's assume, on average, this is a typical mass star that gives out the typical amount of light, so if I know that a portion of the universe is generating this amount of light, I can now say how many stars that would equate to.”
• Now equipped with an estimate of the number of stars within a section of the universe, the next challenge was to work out the size of the universe.

Given we know that the universe is 13.8 billion years old, we can assume that we exist in a sphere 13.8 billion light years in volume. But there's a catch: the universe is potentially infinite in size.

“We know that it has a finite age — we know it started 13.8 billion years ago — but spatially, in terms of its extent, it could be infinite,” Driver says. However we also know that because of its age, we exist in a bubble within that infiniteness, and that bubble is called the 'observable' universe.

1. After all these calculations and caveats, Driver and colleagues came up with a figure of seven followed by 22 zeros, or 70 thousand million, million, million stars in the observable universe.
2. That's 70,000,000,000,000,000,000,000 stars!
3. ^ to top

### So what about grains of sand on Earth?

• “That was almost harder to work out than the number of stars,” Driver says.
• Luckily, someone suggested starting with the Sahara Desert, which is home to around half of all the grains of sand on Earth.
• “That made it easier; I then just had to work out how many grains of sand are in the Sahara, and I didn't have to worry about every beach on the planet,” Driver recalls.
• He found the total size of the Sahara, the average depth of sand across the Sahara and from that was able to calculate the approximate number of grains of sand in the Sahara.

“Once I got all that I could put all those numbers together and got a number that was remarkably close to the figure for the number of stars, but just a little bit less,” he says. “It was about a factor of 10 smaller, but there's easily a factor of 10 error in both of those estimates so it could just as easily be the other way around.”

1. That's 70,000,000,000,000,000,000,000 stars versus 7,000,000,000,000,000,000,000 grains of sand!
2. So even though it's an impossible question to answer definitively, it seems that the mind-bending possibility of so many stars existing in the universe is actually true.
3. Professor Simon Driver spoke with Bianca Nogrady

Be a citizen scientistCan you volunteer some time to be a citizen scientist? Visit Galaxy Explorer and start classifying galaxies for astronomers as part of a real research project. Get involved in August and you could win a wi-fi telescope. Schools' can join in too.

Published 19 August 2015

## Are There More Grains of Sand Than Stars?

This question comes from Sheldon Grimshaw. “I’ve heard that there are more stars in our Universe than there are grains of sand on all the beaches on Earth. Is this possible?” Awesome question, and a great excuse to do some math.

As we learned in a previous video, there are 100 to 400 billion stars in the Milky Way and more than 100 billion galaxies in the Universe – maybe as many as 500 billion.

If you multiply stars by galaxies, at the low end, you get 10 billion billion stars, or 10 sextillion stars in the Universe – a 1 followed by 22 zeros. At the high end, it’s 200 sextillion.

These are mind bogglingly huge numbers. How do they compare to the number of grains of sand on the collective beaches of an entire planet? This type of sand measures about a half millimeter across.

You could put 20 grains of sand packed in side-by-side to make a centimeter. 8000 grains in one cubic centimeter. If you took 10 sextillion grains of sand, put them into a ball, it would have a radius of 10.

6 kilometers. And for the high end of our estimate, 200 sextillion, it would be 72 kilometers across. If we had a sphere bigger than the Earth, it would be an easy answer, but no such luck. This might be close.

So, is there that much sand on all the beaches, everywhere, on this planet? You’d need to estimate the average volume of a sandy beach and the average amount of the world’s coastlines which are beaches.

I’m going to follow the estimates and calculations made by Dr. Jason Marshall, aka, the Math Dude. According to Jason, there about 700 trillion cubic meters of beach of Earth, and that works out to around 5 sextillion grains of sand.

Jason reminds us that his math is a rough estimate, and he could be off by a factor of 2 either way. So it could be 2.5 sextillion or there could be 10 sextillion grains of sand on all the world’s beaches.

## On starry grains

Carl Sagan famously said in his 1980's
television series, Cosmos, that there are more stars in the Universe
than there are grains of sand on all the beaches on Earth. I was reminded
of an article by a friend on this topic while strolling along Woolamai
beach on Australia's southern coast.

The previous night we had been far
enough from Melbourne's midnight glare to see the wonderfully milky strip
of light of our own Galaxy which is so prominent in Southern skies.

A cold
summer night it was and we couldn't stay out for long; but with two friends
visiting us from Finland we managed to get night adjusted quickly enough
to appreciate the sight.

The Milky Way is so bright down under that Northern
hemisphere astronomers on their first trip across the equator have even
mistaken it for bands of clouds! Back on Woolamai beach, a miniscule fraction
of those grains of sand were being whisked into a blizzard by the wind
coming in off the Great Southern Ocean and exfoliating my face; small they
are but sharp and hard. How small and how many on Earth? Well, if you count
a grain of sand as only those which are visible to the naked eye, then
small means about a tenth of a millimeter. How many grains of sand on Earth's
beaches? That's one of those questions where a first estimate can be made
in a few minutes; and give you pause for thought on how to improve it.
Take Australia for example: it's a few thousand kilometers across, so its
coastline is a few tens of thousands of kilometers long (let's say 30,000
kilometers, or 30,000,000 meters). If it were beach all the way round,
the beaches being, say, 50 meters wide and a few meters deep, then we are

30,000,000 x 50 x 5 = 7.5 billion cubic
meters of sand.

A grain of sand is about 0.1 mm across,
so there are 10,000 per meter or 10,000 x 10,000 x10,000 (or 1,000
billion) per cubic meter.

So we are talking (oh so very very roughly)
about 7500 billion billion grains of sand along our Australian coastline.
Call it 10,000 billion billion grains.

So how long are all the coastlines on Earth?
Australia is the smallest of seven continents, so they must be at least
10 times longer when taken alltogether. Let's say a 100 times to keep things
moving along. If that's right, then we have about

10,000 billion billion x 100 = 1 million
billion billion sand grains.

1024 grains of sand. We might
be wrong by quite a few orders of magnitude here, but before getting too
deeply involved in arguing about that, let's forget the sand and move on
to the stars.

How many stars in the Universe? That one
is much easier!

We live in a typical galaxy, the Milky
Way, and we can count its stars with relative ease — it's really just
a matter of peering into space and counting— there are about 100 billion.

And the Universe is filled with galaxies; recently, the Hubble Space Telescope
spent a week staring at a randomly choosen patch of the sky and took a
photo of the brightest galaxies along a path between our own Galaxy and
the edge of the visible Universe.

From that one photo you'd reckon there
are at least 100 billion galaxies in the entire Universe. Putting
both numbers together, we'd expect there to be

about ten thousand billion billion stars
in the Universe

and

about a million billion billion sand
grains
on the beaches of Earth…

Well! There might be more sand grains on
Earth's beaches than stars in the Universe.

But certainly, it's too close
to call! We cannot possible have estimated either figure so well that we
could be sure the stars really are more numerous than the sand grains or
vice versa…

maybe our coastline estiamte was too small, or the beaches
too narrow (or not deep enough). And how many galaxies did we miss with
the Hubble images; small faint ones are out there too, there are new ones
reported every day…

Photo by Latham Jenkins (flickr.com).

Well, yesterday's big World IPv6 Day test seems to have gone off without many—if any—hitches. Hooray!

As we talked about, in the new IPv6 system there are more than 3.4×10^38 or 340 billion billion billion billion (also known as 340 undecillion) unique addresses for computers and other devices that talk over the Internet to use. That's such a ridiculously large number that understanding what it really means is impossible without having something to compare it to.

So, just to get a flavor for how HUGE of a huge number this really is, let's compare it to a number that's often used as an example of an impossibly big number: the number of grains of sand on all of Earth's beaches. But how could we possibly count all of them? Of course, we can't! But we can use some clever thinking to come up with a pretty decent estimate.

To do this, we need to estimate the number of grains of sand in a small volume (say a cubic centimeter), the width and depth of the average beach, and the length of all the coastlines of Earth.

This isn't a super simple task, but it's not impossible either.

And, lucky for us, all the work has been done already! As you can read at that link, when you plug in all the reasonable estimates, you calculate that Earth's beaches contain somewhere between

• 10^20 and 10^24 grains of sand.

For the record, that's somewhere between 300 billion billion (aka, 300 quintillion) and 3 million billion billion (aka, 3 septillion) grains of sand. Yes, that's a pretty wide margin of uncertainty, but there are a lot of variables that go into the calculation…so it's not surprising that the estimate is uncertain.

And yes, that's a pretty impressive number. But compare it again to the 3.4×10^38 addresses in the IPv6 system. When you do that, you'll see that you could actually assign one IP address to every single grain of sand on Earth, and you'd still have enough addresses left over to do the same thing on anywhere from 300 trillion to 300 quintillion identical copies of Earth.

So, yeah, it's a pretty big number!

## Are There More Grains of Sand on Earth or Stars in the Universe?

By Victor Kiprop on November 6 2018 in World Facts

How many stars are in the universe, anyway?

American astronomer Carl Sagan once stated that “there are more stars in our Universe than there are grains of sand on all the beaches on Earth”.

The question left people surprised at how big the universe is considering that the sand along the earth’s coastlines amounts to trillions of tones.

There is no definite way to determine the exact number of stars in the universe and the number of sand grains along the shores but mathematical estimations can be made.

### How Many Stars Are There in the Universe?

Finding the answer to the number of stars in our universe involves generating a mathematical problem of – dare we say it – cosmic proportions. The Milky Way Galaxy has between 100 and 400 billion stars.

There are more than 100 billion galaxies in the universe with some researchers placing the figure at about 500 billion. The lowest number of stars that can be found in the universe is ten sextillion (10 billion billion) and 200 sextillions at the higher end.

These are huge numbers that are incomparable to anything on earth.

### How Many Grains of Sand Are There on Earth?

A single grain of sand found on the beach is half a millimeter in diameter. Twenty grains make up about a centimeter, and 8,000 make up one cubic centimeter. To calculate the volume of sand, you need to determine the amount of coastline that consists of sandy beaches. Dr.

Jason Marshall “The Math Dude” estimates the volume of the beaches to be 700 trillion cubic meters. Mathematically, the figure amounts to five sextillion grains of sand. The mathematician suggests that this is just an estimate and the number could change by a factor of two to a low of 2.

5 and a high of 10 sextillions.