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:
- The Metric System: The metric system is the most "scientific" way to measure capacity. Why? Because the metric system is the universal standard for scientists and mathematicians across the world. Whenever they share the results of their experiments with each other, they use the metric system.
- U. S. Customary Units: The United States predominantly uses U. S. Customary Units, also known as the Imperial system, for everyday measurements which are designed to use other common fractions when converting between measurements.
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:
- A milliliter equals of a liter
- A centiliter equals of a liter
- A deciliter equals of a liter
- A dekaliter equals 10 liters
- A hectoliter equals 100 liters
- A kiloliter equals 1000 liters
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:
- 1 gallon (gal) is made of 4 quarts
- 1 quart (qt) is made of 2 pints
- 1 pint (qt) is made of 2 cups
- 1 cup (c) is 8 fluid ounces (fl. oz)
Here's a relatable guide to help us visualize these amounts:
- A small paper cup of coffee usually measures about 8 fluid ounces
- An average container of ice cream at the grocery store usually measures about 1 pint
- A glass measuring jug you'd find in a kitchen usually measures about 1 quart
- A large plastic container of water at an office water dispenser usually measures about 1 gallon
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:
- When converting larger units to smaller units, we can multiply by an appropriate ratio
- When converting smaller units to larger units, we can multiply by the reciprocal of the same ratio
Topics related to the Capacity
Convert Units of Area and Volume
Flashcards covering the Capacity
Practice tests covering the Capacity
Common Core: 3rd Grade Math Diagnostic Tests
Get additional assistance with capacity
If you're looking for someone to provide your student with extra assistance on all things capacity, we will help. We know that finding a suitable math tutor for your student can be difficult -- so why not let Varsity Tutors handle it for you? We match students with tutors based on scheduling needs, specific learning goals, ability levels, and much more. Reach out today to get started.