# When You’re Stuck in the Sand

Now that it’s summer, 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)).