Length for Class 3

In this chapter, we are going to learn about length. Imagine you have a ribbon or a piece of string. When you measure how much of it you need for a craft project, you are actually measuring its length. Let’s learn more!

What is Length?

The term “length” is used to describe how big something is or how far away it is. It is a way to measure how long or short something is. You can use length to find out how big or small things are. Objects like cars and pencils have a length.

Instruments used to measure length include measuring tape, measuring rulers, measuring our handspan, measuring sticks, etc. We use these instruments to measure the length of objects.

Units of Length

To measure length, we need units. Units are like words that indicate to us how long something is. For example, Katrina's nail cutter of 3 centimetres (3 cm) is shown as:

Here, centimetres is the unit we use to measure the length.

Metric Units of Length

A metric unit of length is a standardized unit of measurement used to measure length or distance.

The following are some important length metric units:

a. Millimetre (mm) 
b. Centimetre (cm) 
c. Metre (m) 
d. Kilometre (km) 

Conversions of Units of length

To make sure everything is accurate and there is no confusion about what is being measured, we need to convert one unit to another.

The conversion of one unit to another is shown as:

Here are some standard length units and how to convert between them:

→ Kilometres (km) to Metres (m):

1 kilometre (km) is equal to 1000 metres (m).
To change kilometres to metres, simply multiply by 1000.
For example: 7 km = 7 × 1000 = 7000 m

→ Metres (m) to Centimetres (cm):

1 metre (m) is equal to 100 centimetres (cm).
To convert metres to centimetres, multiply by 100.
For example: 8 m = 8 × 100 = 800 cm

→ Metres (m) to Millimetres (mm):

1 metre (m) is equivalent to 1000 millimetres (mm).
To convert metres to millimetres, multiply by 1000.
For example: 4 m = 4 × 1000 = 4000 mm

→ Centimetres (cm) to Millimetres (mm):

1 centimetre (cm) equals 10 millimetres (mm).
To transform centimetres into millimetres, multiply by 10.
For example: 3 cm = 3 × 10 = 30 mm

→ Feet (ft) to Inches (in):

1 foot (ft) is equivalent to 12 inches (in).

Note: "Foot" is singular and "feet" is plural.

To change feet to inches, simply multiply by 12.
For example 10 ft = 10 × 12 = 120 in

Example: What is the length in centimetres of the cotton string if its length is 189 metres?

a) 1890 cm
b) 1955 cm
c) 18900 cm
d) 19550 cm

Answer: c) 18900 cm

Explanation: Length in feet of a cotton string = 189 m

Length in centimetres of a cotton string = 189 100 = 18900 cm

Example: Mark has purchased a woollen ball measuring 15 feet long. What is the total length of three woollen balls in inches?

a) 450 inches
b) 540 inches
c) 650 inches
d) 560 inches

Answer: b) 540 inches

Explanation: Total length of a woollen ball = 15 feet
Total length of 3 woollen balls = 15 3 = 45 feet
Total length of 3 woollen balls in inches = 45 12 = 540 inches