How many grains of sand are there on Earth?
The widely quoted answer, about 7.5 × 10^18 grains, is a calculation rather than a count, and it applies to beaches only — not to deserts or the sea floor, which would add at least another two orders of magnitude. The honest uncertainty is a factor of ten in either direction, because every input is a guess about a typical beach. What makes the question worth asking is that the arithmetic is entirely doable on the back of an envelope, and the answer turns out to be smaller than most people expect.
How the figure is arrived at
Three steps. First, grains per unit volume: a medium sand grain is about half a millimetre across, so a sphere of volume 6.5 × 10^-5 cm³; at realistic packing that is roughly 9,000 grains per cubic centimetre, or 9 billion per cubic metre. Second, the volume of the world's beaches: take the world coastline of about 1.6 million km, assume beach along part of it, 30 m wide and a few metres deep of sand. Third, multiply. Change the assumed grain size to 0.2 mm and the answer moves by a factor of fifteen, which is why the result is quoted to one significant figure at best.
How confident it is
- Low estimate
- 1,000,000,000,000,000,000
- High estimate
- 100,000,000,000,000,000,000
- Spread
- 100.0× between the bounds
Other living things and the natural world counts
- How many people are there in the world? about 8.2 billion
- How many ants are there in the world? about 20 quadrillion
- How many trees are there in the world? about 3 trillion
- How many insects are there? about 10 quintillion
- How many species are there? about 8.7 million
- How many people have ever lived? about 117 billion
- How many drops of water are there in the ocean? about 27 septillion
- How many fish are there in the sea? somewhere between 3 trillion and 100 trillion — nobody knows
- How many species are endangered? more than 45,000 assessed as threatened
- How many bees are there in the world? roughly 2 trillion managed honey bees
- How many birds are there in the world? about 50 billion wild birds
- How many bacteria are there on Earth? about 5 nonillion
- How many earthquakes are there each year? about 20,000 located a year — around 55 a day
- How many chickens are there in the world? about 26 billion alive at any moment
Common questions
- How many grains of sand are there on Earth?
- roughly 7.5 quintillion on the world's beaches
- How is that estimated?
- Three steps. First, grains per unit volume: a medium sand grain is about half a millimetre across, so a sphere of volume 6.5 × 10^-5 cm³; at realistic packing that is roughly 9,000 grains per cubic centimetre, or 9 billion per cubic metre. Second, the volume of the world's beaches: take the world coastline of about 1.6 million km, assume beach along part of it, 30 m wide and a few metres deep of sand. Third, multiply. Change the assumed grain size to 0.2 mm and the answer moves by a factor of fifteen, which is why the result is quoted to one significant figure at best.
Related pages
- How many people are there in the world? about 8.2 billion
- How many ants are there in the world? about 20 quadrillion
- How many trees are there in the world? about 3 trillion
- How many insects are there? about 10 quintillion
- How many species are there? about 8.7 million
- How many people have ever lived? about 117 billion
- How many drops of water are there in the ocean? about 27 septillion
- How many fish are there in the sea? somewhere between 3 trillion and 100 trillion — nobody knows
- How many stars are there in the universe? Space and the universe
- How many countries are there in the world? Things people built
- How many bones are in the human body? The human body
- How many stars are there in the Milky Way? Space and the universe
- How many atoms are there in the universe? Space and the universe
- How many galaxies are there? Space and the universe
Sources
- Calculated on this page — At One Place