Measuring Length with Standard Units

When we want to know how long, how tall, or how wide something is, we measure its length. To make sure everyone gets the same answer when measuring, we use standard units and special tools like a ruler or a measuring tape.

Customary Units: Inches and Feet

In the United States, we often use the Customary System to measure length.

• Inches (in): We use inches to measure small objects, like a pencil, a book, or a paperclip.
• Feet (ft): We use feet to measure larger things, like the height of a door, the length of a car, or how tall you are.

Important Rule to Remember: $1 \text{ foot} = 12 \text{ inches}$

If a ribbon is $2 \text{ feet}$ long, it is $24 \text{ inches}$ long because $12 + 12 = 24$.

Metric Units: Centimeters and Meters

Most of the world uses the Metric System. It is also very common in science!

• Centimeters (cm): Like inches, centimeters are used for small objects. A centimeter is smaller than an inch (it takes about two and a half centimeters to make one inch).
• Meters (m): We use meters to measure bigger distances, like the length of a swimming pool or a playground.

Important Rule to Remember: $1 \text{ meter} = 100 \text{ centimeters}$

How to Measure with a Ruler

Measuring is easy if you follow these simple steps:

1. Find the zero: Look at your ruler and find the 0 mark. Make sure you are using the correct side (inches or centimeters).
2. Line it up: Place the 0 mark exactly at one end of the object you are measuring. Do not start at the physical edge of the ruler unless the zero is exactly on the edge!
3. Read the number: Look at where the other end of the object stops on the ruler. The number it lines up with is the length of the object.

Comparing Different Units

Sometimes you might wonder which unit is bigger. For example, which is longer: $1 \text{ foot}$ or $1 \text{ meter}$?

• $1 \text{ foot}$ is $12 \text{ inches}$ (the size of a standard school ruler).
• $1 \text{ meter}$ is about $39 \text{ inches}$ (a little more than $3 \text{ feet}$!).

So, $1 \text{ meter}$ is much longer than $1 \text{ foot}$.