Some objects are long, and some are short.
To tell someone how tall a plant is, you can't just say, "It's as tall as my arm."
You have to use a unit of length, like:
2 feet
Units of length, like feet, are exact lengths everyone agrees on.
Some units are small, like inches.
There are 12 inches in 1 foot.
A paperclip is 1 inch long.
Other units are long, like mile and kilometer.
You measure distances between cities in miles and kilometers.
Different tools help us measure lengths in different units.
You can measure lengths using rulers, measuring tapes, meter sticks and yardsticks.
Hours, seconds and minutes are used to describe time. These are units of time.
Dollars and cents are used to describe money. These are units of money.
In the same way, inches, feet, and yards are used to describe length. These words are called units of length.
Some common units of length are centimeters, inches and meters.
Let's learn about the seven most common units of length.
A centimeter is a small unit of length. It is usually used to measure small objects.
The symbol, or abbreviation, for centimeters is cm.
You may have seen centimeters marked on a ruler or a measuring tape.
The length of an eraser is about 5 cm.
The length of a paper clip is about 2 and a half cm.
An inch is another small unit of length. It's also used to measure small objects.
The symbol for inches is ". You can also write in.
An inch is about 2 1/2 times bigger than a centimeter.
In other words,
1" = about 2 1/2 cm
Inches are also marked on rulers and measuring tapes.
The length of a paper clip is about 1".
The length of a book is about 11".
A meter is a big unit of length. It is usually used to measure large objects.
The symbol for meters is m.
1 meter has 100 centimeters inside it.
In other words,
1 m = 100 cm
Measuring tapes and meter sticks are used to measure lengths in meters.
Some examples of lengths in meters are:
Length of a car is about 5 m.
Length of a pine tree is about 18 m.
Length has some other units, like foot (ft), yard (yd), kilometer (km) and mile (mi).
We use feet if there is more than 1 foot.
12 inches make 1 foot (ft).
1 ft = 12"
Tip: you can also write 6 feet as 6' or 6'0".
Can you figure out how many inches are in 2 feet?
That's right. There are 24 inches in 2 feet.
1' = 12"
2' = 24"
3' = 36"
3 feet make 1 yard (yd).
1 yd = 3 ft
Yardsticks are used to measure lengths in yards.
Yardsticks are 1 yard long.
A kilometer (km) is an even bigger unit of length than feet, yards and meters.
1,000 meters makes 1 kilometer.
1 km = 1,000 m
People who drive long distances measure the distance in kilometers.
Like the kilometer, a mile is also a very big unit of length.
About 1 and 1/2 kilometers make 1 mile.
1 mile = about 1 1/2 km
In the United States, people use miles, but in the rest of the world, they use kilometers.
Great work. Now you know the most common units of length.
Units of length are lengths everyone agrees on.
The units of length most used in the United States are: inches, feet, yards, and miles.
Tip: These are called the Customary System units.
12 inches = 1 foot
3 feet = 1 yard
1760 yards = 1 miles
The units of length used most in the rest of the world are: centimeters, meters, and kilometers.
Tip: These are called the Metric System units.
100 centimeters = 1 meter
1,000 meters = 1 kilometer
It's important to know the units in both systems.
Start the practice to help you memorize them all.