How many grains of sand are on all of Earth's beaches?
Sand grains are roughly half a millimetre across, and beaches wrap around every continent on the planet. Scientists have tried to turn that into an actual number by estimating average grain size and total beach volume, then scaling up. Take a guess at the order of magnitude.
Reveal the answer
One widely cited estimate puts it at around 4 x 10^20 grains, 400 billion billion, just for beaches, before counting deserts or riverbeds. Estimates from different methods vary by orders of magnitude, but all of them land somewhere in the hundreds of billions of billions.
— Scientific American, Do Stars Outnumber the Sands of Earth's Beaches?