Now that it’s June, lots of people are thinking about going to the beach. So our fan Sophia Y. asked, how many sand particles would it take to cover a person? First, there’s a grown-up formula to figure out how much area your skin covers! (you multiply your weight and height by other numbers, to start). We tried it for a regular-sized 6-year-old (50 pounds, 42 inches tall), and got 8 ½ square feet of skin area. A medium-sized grown-up woman has about 18 square feet, and a man has more than 20 sq ft. Each grain is 1/1,000th of a foot wide, so it takes 1,000 x 1,000 or about 1 million grains of sand to cover just 1 square foot. That’s just a thin layer of single grains…if you want a few inches of sand, you need hundreds of layers, giving us over a billion grains for a grown-up! Luckily the beach has plenty of sand for the job.
Wee ones: If your body has 7 square feet of skin and your friend has 5 square feet, who needs more sand to be totally covered?
Little kids: If your whole body has 8 square feet of skin, and each arm takes up 1 square foot of that and each leg takes up 2 square feet, what does that leave for your torso (the part in the middle)? Bonus: How much more area would you need to reach 10 square feet?
Big kids: If you dig out 20 cubic feet of sand (imagine perfect cubes 1 foot wide), then shovel 8 cubic feet back into the hole, then dig out 4 cubic feet, then dump 1 cubic foot back in…how many cubic feet have you dug out in total? Bonus: If you now make the hole twice as wide and twice as long (with same depth), how much sand have you dug out in total? (Hint if needed: What if you made it just twice as wide?)
The sky’s the limit: If you’re covering a teenager with 16 square feet of skin total 3 inches deep in sand, how many billions of grains do you need — and how do you write that in digits? (Remember, the area facing up is just half of that, and you need 1 billion grains for each cubic foot (12 inches deep)).
Wee ones: You have more.
Little kids: 2 square feet, since your arms and legs take up 6. Bonus: 2 more square feet.
Big kids: 15 cubic feet. Bonus: 60 cubic feet. It would be just 30 cubic feet if you doubled in only one direction.
The sky’s the limit: 2,000,000,000 grains of sand (2 billion). You’re covering just 8 square feet of skin, and if you went 1 foot deep, you would need 8 billion grains. But 3 inches is only 1/4 as deep, so you need only 1/4 as many grains as that.
And one helpful tip for the beach: if you’re covered in wet sand, just rub talcum powder into it. The powder soaks up the water making the sand stick, and it will all fall off!