5 Tips for Understanding Weights and Measures

Are you baffled by the overwhelming variety of weights and measures we face in daily life? You know, the myriad methods by which we quantify things like volume and mass?

If you’re not sure about the difference between millileters, fluid ounces, tablespoons, and gallons, then rest assured that you are not alone. And if your intuition about grams, ounces, pounds, and tons is not exactly top-notch, either, then join the club! The ailment that’s afflicting you is more common than the common cold.

The good news is that there is a cure! Today, we’re going to take a look at 5 quick and dirty tips that will help you make sense of the world of weights and measures.

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Tip 1: Fluid Ounces

Did you know that both mass and volume can be measured in ounces? Well, sort of. In truth, the volumey kind of ounces are more properly known as “fluid ounces.” And 1 fluid ounce is…not much. How much exactly?

Remember medicine cups? I know, how could you possibly forget those wonderful little vessels of delight. As it turns out, a standard medicine cup holds 1 fluid ounce of liquid. If you’re of a certain age, you may be more familiar with a slightly larger piece of glassware known as a shotglass. How much do they hold? Typically up to 2 fluid ounces.

Tip 2: Non-Fluid Ounces

If fluid ounces measure the volume of fluids, then regular ounces must measure…what exactly? Well, as you probably know, we weigh babies (and bigger people, too) using pounds and ounces. So the regular old non-fluid ounce must be a measure of mass (which, as we’ve learned, is related to—but not exactly the same as—weight.)

How much is 1 ounce? It’s 1/16 of a pound, of course! But that doesn’t give us much of an intuitive feel for things, so let’s try to latch onto something a bit more memorable. How about this: According to Wolfram Alpha, a pencil and an empty soda can each weigh about 0.5 oz., and a tennis ball weighs about 2 oz.

Tip 3: Why Both Ounces?

An obvious question that might come to mind at this point is: Why is the same word—ounce—used to measure two different things? The historical chain of events that led us to this dilemna is long and complicated. But there is, thankfully, a simple reason that we can state that should summarize things nicely–and even shed some light on the situation.

The key thing to know is that 1 fluid ounce of water weighs pretty close to 1 ounce. And that coincidence isn’t a coincidence, at all: in fact, it’s the reason that we use the same word to describe these two very different things.

Tip 4: Pints, Quarts, and Gallons (Oh My!)

Since 1 fluid ounce is a pretty tiny amount of liquid (as evidenced by the dinky medicine cup,) it’s no wonder that we commonly use larger units to measure volumes of everyday things like beverages and gasoline. For example, 8 fluid ounces of a liquid is known as 1 cup—a fact which those of us who use measuring cups to cook with are no doubt intimitely acquainted with.

Creating new units of volume is fun, so people didn’t stop there.

Creating new units of volume is fun, so people didn’t stop there. Two cups is also known as 1 pint which–fun fact–is roughly the volume of air that humans inhale and exhale during a typical breath. It’s also the most common size of a paper carton of cream or half-and-half.

Marching up this liquid ladder, two pints (which is also 4 cups) is known as 1 quart, and 4 quarts is known as 1 gallon. Notice that the word “quart” is part of the word “quarter”—can you guess why? It’s because it’s a quarter gallon! A quart is the size of those tall, skinny, paper milk cartons, a half gallon is the size of the wider paper milk cartons, and 1 gallon is the size of a large plastic jug of milk. Thirsty?

Tip 5: What About Millileters?

Of course, the fluid ounce isn’t the only way we measure volume. In fact, most of the world uses an entirely different system to do so! It’s called the metric system, and it’s what all the cool kids are using these days. In this system, we measure volume using liters and millileters. One liter is made up of 1,000 millileters, so it’s very easy to do calculations and convert back and forth between either.

What does a millileter look like? If you’re familiar with teaspoon and tablespoon measurements, then it’s helpful to know that 1 teaspoon is about 5 millileters (abbreviated 5 mL.) So 1 millileter is a bit less than a quarter teaspoon. Like a fluid ounce, a millileter isn’t very much volume. 

And that’s exactly why we don’t often use millileters when buying bottles of refreshing beverage items from the grocery store, or fuel for our cars. Instead, we use the millileter’s big sibling, the liter. Soft drinks are often sold in 1- and 2-liter bottles, and in Europe and much of the rest of the world, gasoline is priced and sold by the liter.

Just in case you’re wondering, there are 3.785 liters in 1 gallon.

Wrap Up

OK, that’s all the weights and measures we have time for today—but rest assured, it’s a topic we’ll be returning to soon!

Please be sure to check out my book, The Math Dude’s Quick and Dirty Guide to Algebra. And remember to become a fan of The Math Dude on Facebook, where you’ll find lots of great math posted throughout the week. If you’re on Twitter, please follow me there, too.

Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!

Weights image courtesy of Shutterstock.