Every day we stand up and walk around on the ground. That’s because we aren’t fish. But 3/4 of Earth is covered with water. So our friend Parker M. asked, how much does the ocean weigh? Well, water’s really heavy: if you had a box 1 foot wide, 1 foot long and 1 foot tall filled with water, it would weigh about 62 1/2 pounds! Scientists’ best guess is that there are 326 million cubic *miles* of water, meaning boxes a whole mile wide, a mile long and a mile tall. Each side of a cube that size is 5,280 feet long, so there are 5,280 x 5,280 x 5,280 little 1-foot boxes in each of those cubic miles…we get 47,986,532,352,000,000,000 of those, or nearly 48 *quintillion*. Multiply by 62 1/2 pounds for each of those, and that weighs 3 *sextillion* pounds. We’re glad we could figure this out without weighing it cup by cup!

*Wee ones:* Plug a sink, turn on the water while you count to 5, then turn it off. Is the sink a little bit full, half full, or totally full?

*Little kids:* If you drink a cup of water at breakfast, then lunch, then dinner, plus 3 more cups in the afternoon, how many cups do you drink each day? *Bonus:* How many more would you need to drink a half-gallon (8 cups)?

*Big kids:* 1 gallon of water weighs about 8 pounds. How many gallons of water match your weight? (Hint if needed: 8 is 2 x 2 x 2, so to divide by 8, you just cut in half 3 times in a row.) *Bonus:*How much does a 40-gallon bathtub of water weigh, if each gallon weighs about 60 pounds?

Answers:

*Wee ones:* It should probably be only a little bit full.

*Little kids:* 6 cups. *Bonus:* 2 more cups.

*Big kids:* Different for everyone…divide your weight by 8, or see how many 8s you need to add up to match your weight. *Bonus:* 2,400 pounds!

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.