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Capacity

Capacity is the ability of an object to hold other objects. You're probably already aware of how this works! There are only so many books you can stuff into your backpack. If you pour too much water into your water bottle, it will overflow. In the world of mathematics, we can measure capacity accurately with specific types of measurements. Let's find out how:

How we measure capacity

There are two possible ways to measure capacity:

Measuring capacity with the metric system

We measure capacity in liters according to the metric system. Like other metric units of measurement, liters can be further divided into smaller or larger units based on powers of ten.

For example:

Of these measurements, milliliters and liters are especially common.

We can see that this eyedropper has 2 milliliters:

Measuring capacity in U. S. customary units

We measure capacity in fluid ounces, pints, quarts, and gallons according to U. S. customary units and the Imperial system of measurement. As you will see, these measurements are far less uniform and "predictable" compared to measures of capacity in the metric system:

Here's a relatable guide to help us visualize these amounts:

Here is a jug of water that measures 2 cups. This is equal to 1 pint:

Hold on a minute.. What exactly is a cup according to U. S. customary units?

A cup is another unit of measurement in the Imperial system, and it usually equals about 8 fluid ounces.

It's important to note that some people might say that a cup is equal to 250 ml. However, if you convert 8 fluid ounces to ml, you get a value of about 236.5 ml instead. While this discrepancy highlights the potential for confusion when converting measurements between metric and U. S. customary units, with practice, navigating these conversions can become more straightforward.

Converting measurements of capacity

The metric and Imperial systems have units of capacity that are roughly correlated. One example involves liters and pints. A liter measures 2.113 pints, allowing us to make approximations between the two measurements fairly easily by rounding down to 2 pints per 1 liter. A fluid ounce also measures 29.574 milliliters, so we can round up to 30 milliliters per 1 fluid ounce.

That being said, we need to remember that approximations can make our end results surprisingly inaccurate when they are multiplied over the course of numerous steps in an operation. It's easy to end up with a final result that is inaccurate by thousands of milliliters if we're not careful! This is why it's always a good idea to round up or down with our final result rather than with our initial data.

Unit analysis can also help us convert between U. S. customary and metric measurements for capacity. This can help us address some of the confusion we saw earlier.

We know that a glass of milk contains more than an eyedropper but less than a small pitcher. We also know that a small pitcher can hold about 4 glasses. If a small pitcher measures 1,000 milliliters, all we need to do is divide by four to get our answer: 250 ml.

Here are some additional rules for converting measures of capacity:

Topics related to the Capacity

Volume

Customary Units

Convert Units of Area and Volume

Flashcards covering the Capacity

3rd Grade Math Flashcards

Basic Arithmetic Flashcards

Practice tests covering the Capacity

Common Core: 3rd Grade Math Diagnostic Tests

3rd Grade Math Practice Tests

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