Measuring Length

Length is a measure of how long something is. We use rulers or tape to measure length. We most of the time measure length in millimeters, centimeters (cm), meters (m) and kilometers (km) as unit of length. Millimeters and centimeters are used to measure short lengths. Long lengths are measured in meters. The distance between two far off places is measured in kilometers (km)

Example: The length of a pencil is measured in centimeters, Length of bed in meters, while the distance between two places is measured in kilometers.

Important points

      1.   The standard unit of length is ‘Meter’.

      2.   We use ‘cm’ for centimeter, ‘mm’ for millimeter, ‘m’ for meter and ‘km’ for kilometer in short form.

      3.   1 centimeter length is equally divided into 10 small parts and each part is called millimeter (mm).

Thus, 1 cm = 10 mm or 10 mm = 1 cm

      4.   1 meter length is equally divided into 100 small parts and each part is called centimeter (cm).

Thus, 1 m = 100 cm or 100 cm = 1 m

      5.   1 kilometer length is equally divided into 1000 small parts and each part is called meter (m).

Thus, 1 km = 1000 m or 1000 m = 1 km

Addition and Subtraction of units of length

Arrange the number in column according to the units. First add smaller unit then add larger unit.

Example 1:

Add 24m 14cm and 35m 13cm

Example 2:

Subtract 14m 13cm from 35m 13cm

Example 3:

A shopkeeper had 250m long rope. 190m was sold. What is the length of the rope left?

Solution:

Length of rope = 250m

Length of rope sold =190m

Length of rope left = 250m – 190m

Conversions:

To convert meters into centimeters, we multiply the given number of meters by 100.

Example 1: Convert 5m into cm

5m = 5 x 100

     = 500cm

Example 2: Convert 4m 85cm into cm

4m 85cm = 4 x 100cm + 85cm

              = 400cm + 85 cm = 485 cm

To convert kilometers into meters, we multiply the given number of kilometers by 1000.

Example 1: Convert 15km into m

15m = 15 x 1000

       = 15000m

Example 2: Convert 4km 850m into m

4km 850m =4 x 1000m + 850m

                 = 4000m + 850m

                 = 4850m