How To Weigh Grams With No Scale

If you don't have a proper scale, don't despair. Should you find yourself in a pinch, you can make your own scale with some pocket change, a pencil, and a regular old ruler. The key is in the fact that many common objects have specific standard weights, such as coins. And while you won't have much luck with a college-level project without well-calibrated, professional instruments, DIY scales can provide surprisingly accurate measurements in grams.

For this exercise, tape will also come in handy, though it's not necessary. Two small cardboard squares of equal size or paper cups can also be helpful to provide dishes to hold the weights, all of which are common supplies that you'll find in a set of standard desk accessories. 

The accuracy of your DIY scale depends on the weights of the coins you use. Every country's metal currency has its own standard composition and weights; here we're using coins from the United States, but you can also use other currencies. Simply substitute the values of the coins within the process, and a quick web search should provide your specific coins' masses to an accurate degree.

Before you construct your own scale, search the web for the weights of the currency you plan to use. For United States coins, you can refer to the official standards of the U.S. Treasury. According to the U.S. Mint, each penny weighs 2.500 grams, each nickel weighs 5.000 grams, each dime weighs 2.268 grams, and each quarter weighs 5.670 grams.

As you can see, United States coins are minted to an accuracy of a thousandth of a gram. Of course, metal wears down over time, and many coins pick up grime that can affect their weights. Thus, it's a good idea to clean the dirty coins and refrain from using really well-worn ones. Furthermore, you should only consider your scale's accuracy to be about 1/10th of a gram to be safe. 

The steps to build a scale from scratch are straightforward. Start by placing a pencil on a flat surface and balance your ruler on top of it perpendicularly (for a 12-inch ruler, for example, the 6-inch mark should help you find the center of mass). Next, you can place a piece of tape along the place where the ruler rests on top of the pencil to prevent it from slipping. It should maintain its balance so that the ruler is not touching the surface. Optionally, you can tape or glue paper cups or cardboard squares to both ends of the ruler to create bases to place your weights. Make sure the ruler remains balanced atop the pencil even with the dishes attached — they'll have to be equidistant from the center of mass, so it's a good thing your scale's central beam is a ruler!

Once your DIY scale is set up and balanced, simply place the object you want to weigh on one end of the scale and place your coins, one by one, on the other end. When you find the right combination of coins to balance the scale — meaning the ruler no longer touches the surface — you can then add up the known weights of the placed coins to find the mass of the object.

For example, if you place a grape on one end of the ruler, you can test how many coins it takes to reset the ruler to a balanced, horizontal position. If it requires two dimes and a penny to return the system to balance, you simply have to add the standard masses of the coins to find out the weight of the grape. The two dimes weigh 4.6 grams in total (2.3 grams multiplied by two) and the penny weighs 2.5 grams. Thus, the three coins — and therefore the grape — have a total mass of 7.1 grams. That's a chunky grape!

Keep in mind that this design isn't perfect. For one, a pencil has flat sides that can settle into a seemingly balanced position, even when the ruler isn't actually perfectly balanced. Furthermore, the items that you place on your DIY scale must have centers of masses that are equidistant from the center of the scale. It's nearly impossible to achieve such perfect orientations, especially when you're weighing objects with asymmetry. Nonetheless, this scale should give you a good idea of the mass of your objects — volume and density are a whole different measurement. You will have to experiment with different combinations and quantities of coins to find the balance, but don't give up. 

If you or your kids like this DIY project, there are tons of other 10-minute science projects that you can do at home.