5 Tips for Understanding Weights and Measures

How much is a fluid ounce? How about a milliliter? Or a gallon? If you don't have an intuitive feel for exactly how much volume these quantities represent, keep on reading!

Jason Marshall, PhD
4-minute read
Episode #209

WeightsAre 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.


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.


About the Author

Jason Marshall, PhD

Jason Marshall is the author of The Math Dude's Quick and Dirty Guide to Algebra. He provides clear explanations of math terms and principles, and his simple tricks for solving basic algebra problems will have even the most math-phobic person looking forward to working out whatever math problem comes their way.