# How Sandbags Work

Science | Natural Disasters

## Playing in the Sand: Fill'er Up

Ready to start fighting back floodwaters? First, you'll want to have an idea of how many sandbags you need. Using specifications set up by the U.S. Army Corps of Engineers, imagine this. You want to build a wall that's 4 feet (1.2 meters) high by 10 feet (3 meters) wide. The wall should be in a pyramid shape -- we'll discuss the reason you build a pyramid in the next section. What's important to know here is that you will need 78 sandbags for each foot of that wall [source: Leibenluft].

Now, let's get filling. Sandbags should only be filled one-half to two-thirds full so there will be room to tie the bag or fold over the top. Again, you want your bag to weigh around 40 pounds (18 kilograms) so that the sand has room to move around. This is key when the bags are laid down, as you want them to mold together into a seamless wall. Teams of two to three volunteers can easily fill sandbags, taking simple safety precautions, such as wearing gloves to handle the chemically treated bags. Goggles are helpful, too, especially if it's a windy day. After that, it's just common sense -- one person holds the bag open with the second person adding the sand to the bag. If there are three people on the team, the third person can pile the filled sandbags.

You may wonder how many grains of sand it takes to make a 40-pound sandbag. It depends on how fine or coarse the sand is. But to get an idea, one measuring cup holds about 12.5 ounces (0.35 kilograms) of sand, give or take. You'd need to scoop around 51 cups of sand to fill your bag. Thankfully, volunteers use shovels, not measuring cups!

Though manually filling sandbags is the easiest and least expensive method, it's also the most time-consuming. Automated options exist for times when you need to quickly produce a substantial number of sandbags. Bag-holding racks, funnels on the backs of dump trucks, and other commercial equipment can speed up the process. This equipment isn't always available -- especially in emergency situations or areas that are difficult to reach. Numerous companies sell prefilled sandbags, and an online search yields multiple opportunities to buy them, in case you live in a flood-prone area and want to stack some away for a rainy day.