How to Measure & Calculate Elapsed Time

Instructor: Ashley Pettway

Ashley is a Special Education teacher who loves inquiry-based, hands-on learning!

Time is constantly passing, but how can we calculate how much time is passing? In this lesson, we'll learn what elapsed time is and explore two ways to measure and calculate it.

What is Elapsed Time?

Elapsed time is the amount of time that has passed between two given times. At the end of this lesson, you'll be able to calculate how long it takes you to do something or how long until something starts. So let's get started!

Types of Clocks

You know that clocks are used to tell time. There are two main types of clocks that we see every day. Let's learn about them now.

analog and digital clock

Analog Clock: A circle with numbers 1-12 written around the edges and at least two moving hands

Digital Clock: A clock that displays the time with three or four digits

We'll start by using the analog clock to calculate elapsed time just because it's a better visual example.

Elapsed Time on an Analog Clock

Remember, on an analog clock, the short hand points to the hour, and the long hand points to the minutes. In the picture showing both kinds of clocks, the analog clock reads 7:47. As the long hand moves around the clock, it touches each short line. These are equal to one minute. The numbers represent five minutes passing. After the long hand makes one full circle and 60 minutes pass, the short hand moves to the next number showing that one hour has passed.

Example

Let's give it a try! Jeremiah arrives at school at 8:15 AM. He is doing a special project in science, and he is very excited. Science begins at 11:41 AM. How long does Jeremiah have until his science class begins?

elapsedtimeanaloggraphic

Pay close attention to the colors. The blue represents the hours, and the red represents the minutes. Let's start with the hours. The blue hand moved three hours, from 8 AM to 11 AM. The red hand moved 26 minutes. You can count each tiny mark, or you can count by fives and add one more minute. Jeremiah has 3 hours and 26 minutes until his science class begins.

Always go back and check your work. It's very easy to add too many hours when counting around the clock.

Elapsed Time Mountain Strategy

Now we will learn a different way to measure and calculate elapsed time. This works for analog and digital clocks. You'll actually make a timeline to show the time that has passed. Here's how it works:

Mountains = 1 hour

Hills = minutes in multiples of 5 (5, 10, 15, 20, and so on)

Rocks = 1 minute

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