U.S. customary units: fluid volume

Let's do a survey about how we would measure the volume of fluids under US customary units. So the smallest volume of fluid that you'll hear people talk about-- and this will often be in cooking recipes or something like this-- you'll talk about a teaspoon. And most of us have teaspoons that are roughly the size of a teaspoon in our cupboards someplace. So this recipe might call for a teaspoon of sugar, or a teaspoon of salt, or a teaspoon of oil. And you've seen what it looks like. But those are the smaller spoons that you might have in your cabinets in your kitchen at home. So this might be a teaspoon right over here. Now, if you were to take 3 teaspoons together, you have something else that you would probably have in your cabinets. So if we multiply this volume, so let's say this right over here is a teaspoon. This right over here is a teaspoon of some substance. If you multiply that by 3, then you get to the tablespoon. So 3 teaspoons equal 1 tablespoon. So a tablespoon's going to be a little bit bigger. So a tablespoon might look like this. These tend to be about the size of the larger spoons that you have in your cupboard, so a tablespoon, just like that. So if you have 3 times the fluid, you get to a tablespoon. Now, if you take 2 tablespoons, put them together, then you get to the ounce. And I have to be careful here. You get to the fluid ounce. And the US customary units, they aren't designed to be super, super clear. Because you also have the ounce as a measure of weight. You have the ounce that is a measure of weight, which is equal to 1/16 of a pound. And now you have a fluid ounce, which you could either view as 2 tablespoons or, as we'll see, 1/8 of a cup. Now, you might say, well, why are they both called ounces? What's the relationship between the two? Well, there is somewhat of a relationship between the two. If you took a little bit over an ounce of water, so a weight of ounce of water, slightly over an ounce of water, that volume is going to be about a fluid ounce. An ounce of water in weight and a fluid ounce of water in volume are very, very, very close, although they aren't exactly the same thing. Now, if you think about, what would you measure here? We already talked about recipes, and teaspoon, tablespoon, fluid ounce. You might be thinking about how much medicine maybe someone might take. Maybe they need to take 2 tablespoons, which would be equivalent to a fluid ounce. Now, if you take 8 fluid ounces and put them together-- so let me draw a fluid ounce here just so we still have drawings. So you could imagine some medicines have a little cap on the top that you could put the medicine in. So if you do 2 tablespoons in it, maybe that will be a fluid ounce. Now, if you take 8 fluid ounces then you get to a cup. And many of us have this in our kitchens. We have a measuring cup that will measure exactly a cup. And you might have a recipe for pancakes that say, hey, put a cup of flour in there. And also a lot of the cups that you have in your house might be around might be around the size of a cup. If you look at, say, a can of soda that you're probably familiar with, a can of soda, the typical can of soda, is 12 ounces, not 8 ounces. So a typical can of soda is a cup and a half. We see that a cup is 8 fluid ounces. A typical can of soda is 12 fluid ounces. So it is equivalent to a cup and a half. Let me make sure this looks like a can of some kind. So if this was 12 ounces, this is 1 and 1/2 cups. But it gets you a sense of how much fluid volume a cup actually is. Now, if we were to take 2 cups, now you're dealing with a pint. And so you might have seen pints. Sometimes they're in these small cartons. So a pint might look something like this in a carton. That looks more like a house. But I think, hopefully, you get the picture that this is intended to be a carton of some kind. So you have something like that. And so the pint, it's 2 cups. And so let's say this is the fluid inside of it. Let's say this was transparent, and you might see it there. Or if you have a very large mug, that might be the size of a pint, so if you have a very large mug like this. So my best attempt at drawing a large mug, this might be roughly equal to a pint. So let me put some fluid in here. So there you go. There's my large mug. It's got a pint. Now, if you take 2 pints, now you are dealing with a quart. And you might have found yourself going to your local convenience store and buying a quart of milk. A quart of milk, those are kind of those longer but still kind of skinny looking-- so it might look something like this. I'm trying to draw a carton of a quart of milk. And then finally, if you were to take 4 quarts together, you get to a gallon. So you take 4 quarts together-- so times 4-- you get to a gallon. So we're most familiar with a gallon of milk. So let me see if I can draw a gallon of milk here, my best attempt. Well, I'm sure someone could draw a better gallon of milk here. But at least in the US, it tends to be one of the most typical ways that they sell milk. And it has, oftentimes, a little red or orange thing right on top there, so a gallon of milk. So just to review things, right here, I just multiplied from the smaller unit to the larger one. But if you want to think about everything in terms of ounces, that's one way to think about it. A cup right over here is equal to 8 ounces. 8 ounces is equal to a cup. If you multiply that by 2, then you get to 16 ounces is equal to a pint. If you multiply that by 2, you get 32 ounces. 32 ounces is equal to a quart. And if you multiply that times 4, you get 30 times 4 is 120, plus 8. You get 128 ounces per gallon. And so next time you go buy something in the supermarket, I encourage you to look at how it's being measured. And you'll see that oftentimes you might buy a quart of milk, but they'll also say that this is a 32-ounce container. And in this context, they're talking about fluid ounces.