Grade 4
  1. Numbers and Place Value  1.1. Understanding Place Value  1.2. Reading and Writing Large Numbers  1.3. Comparing and Ordering Numbers  1.4. Rounding Numbers  1.5. Understanding Odd and Even Numbers  1.6. Number Patterns and Sequences
  2. Addition and Subtraction  2.1. Addition of Large Numbers  2.2. Subtraction of Large Numbers  2.3. Estimation in Addition and Subtraction  2.4. Word Problems on Addition and Subtraction
  3. Multiplication and Division  3.1. Understanding Multiplication  3.2. Multiplying Multi-Digit Numbers  3.3. Understanding Division  3.4. Dividing Multi-Digit Numbers  3.5. Multiplication and Division Facts  3.6. Word Problems on Multiplication and Division
  4. Factors and Multiples  4.1. Understanding Factors  4.2. Finding Common Factors  4.3. Understanding Multiples  4.4. Finding Common Multiples  4.5. Prime and Composite Numbers  4.6. Prime Factorization  4.7. Greatest Common Factor  4.8. Least Common Multiple
  5. Fractions  5.1. Understanding Fractions  5.2. Equivalent Fractions  5.3. Simplifying Fractions  5.4. Comparing and Ordering Fractions  5.5. Addition of Fractions  5.6. Subtraction of Fractions  5.7. Mixed Numbers and Improper Fractions  5.8. Converting Mixed Numbers to Improper Fractions  5.9. Word Problems on Fractions
  6. Decimals  6.1. Understanding Decimals  6.2. Reading and Writing Decimals  6.3. Comparing and Ordering Decimals  6.4. Rounding Decimals  6.5. Addition of Decimals  6.6. Subtraction of Decimals  6.7. Converting Decimals to Fractions  6.8. Converting Fractions to Decimals  6.9. Word Problems on Decimals
  7. Measurement  7.1. Length  7.1.1. Units of Length  7.1.2. Converting Units of Length  7.1.3. Perimeter  7.1.4. Area  7.1.5. Word Problems on Length  7.2. Weight  7.2.1. Units of Weight  7.2.2. Converting Units of Weight  7.2.3. Word Problems on Weight  7.3. Volume and Capacity  7.3.1. Units of Volume  7.3.2. Converting Units of Volume  7.3.3. Estimating Volume and Capacity  7.3.4. Word Problems on Volume and Capacity  7.4. Time  7.4.1. Reading Time  7.4.2. Units of Time  7.4.3. Converting Units of Time  7.4.4. Calculating Elapsed Time  7.4.5. Word Problems on Time
  8. Geometry  8.1. Properties of Shapes  8.1.1. Types of Angles  8.1.2. Types of Triangles  8.1.4. Symmetry  8.1.5. Lines of Symmetry  8.2. Perimeter and Area  8.2.1. Perimeter of Rectangles  8.2.2. Perimeter of Other Shapes  8.2.3. Area of Rectangles  8.2.4. Area of Other Shapes  8.2.5. Area of Irregular Shapes  8.3. Coordinate Geometry  8.3.1. Understanding Coordinates  8.3.2. Plotting Points on a Grid  8.3.3. Identifying Shapes on a Grid
  9. Data and Graphs  9.1. Types of Data  9.2. Organizing Data  9.3. Reading Bar Graphs  9.4. Drawing Bar Graphs  9.5. Line Plots  9.7. Reading and Interpreting Line Graphs  9.8. Word Problems on Graphs
  10. Money  10.1. Understanding Money  10.2. Addition and Subtraction with Money  10.3. Making Change  10.4. Multiplying and Dividing Money  10.5. Word Problems on Money

Grade 4 → Measurement → Length ↓


Units of Length


Length is the way we measure the distance from one point to another. It tells us how long or wide something is. In our everyday life, we come across different objects of varying lengths and need to measure them for accuracy. We use specific units to measure these lengths. In this explanation, we will explore the different units of length, how they can be converted into each other, and some examples to understand the concepts better. Let’s dive into it.

Basic units of length

The basic units of measurement are part of the metric system and the customary system. The metric system is widely used around the world, except in some countries like the United States, where the customary system is more prevalent. Let's take a look at the basic units in both systems.

Metric system

The metric system is based on the number 10, which makes it very convenient to use. The basic units of length in the metric system are:

  • Millimeter (mm): The millimeter is the smallest unit of length in the metric system. It is often used to measure very small objects.
  • Centimetre (cm): There are 10 millimetres in a centimetre. Centimeters are used to measure small objects, usually in day-to-day transactions. For example, the width of a pencil or the height of a notebook can be measured in centimetres.
  • Meter (m): A meter is made up of 100 centimeters or 1000 millimeters. It is the basic unit of length in the metric system, used to measure medium distances, such as the length of a room or the height of a tree.
  • Kilometer (km): There are 1,000 meters in a kilometer. Kilometers are used to measure long distances, such as the distance between two cities.

Visual example

Here are the measurements of these units, from millimeters to kilometers:

1 mm1 cm = 10 mm1 meter = 100 cm1 km = 1000 meters

Customary system

The traditional system is used mainly in the United States. The basic units of length in this system are:

  • Inch (in): The inch is the smallest unit of length in the traditional system. It is usually used to measure small lengths, such as the length of a pencil or the width of a book.
  • Foot (ft): A foot is equal to 12 inches. Feet are often used to measure the height of a person, the length of a piece of furniture, or the width of a small room.
  • Yard (yd): A yard is equal to 3 feet or 36 inches. It is used to measure medium distances, such as the length of a football field.
  • Mile (mi): A mile is equal to 5,280 feet or 1,760 yards. Miles are used to measure long distances, such as the distance between one city and another.

Visual example

In the traditional system the units of length increase as follows:

1 in1 feet = 12 inches1 yard = 3 feet1 mile = 1,760 yards

Converting units of length

Sometimes it is necessary to convert from one unit of length to another to make a measurement meaningful or to perform a calculation. Let's learn how to convert between units in both the metric system and the customary system.

Conversion to the metric system

Since the metric system is based on multiples of 10, conversions are simple. Here are some basic conversions:

  • Millimeters to Centimeters: Divide the number of millimeters by 10 because there are 10 millimeters in 1 centimeter.
  • Centimeters to Meters: Divide the number of centimeters by 100 because there are 100 centimeters in 1 meter.
  • Meters to kilometers: Divide the number of meters by 1,000 because there are 1,000 meters in a kilometer.
Example: Convert 2,500 millimeters to meters. Step 1: Convert millimeters to centimeters: 2,500 mm ÷ 10 = 250 cm Step 2: Convert centimeters to meters: 250 cm ÷ 100 = 2.5 m Therefore, 2,500 millimeters equals 2.5 meters.
Example: Convert 2,500 millimeters to meters. Step 1: Convert millimeters to centimeters: 2,500 mm ÷ 10 = 250 cm Step 2: Convert centimeters to meters: 250 cm ÷ 100 = 2.5 m Therefore, 2,500 millimeters equals 2.5 meters.

Conversion to the customary system

Converting between units in the traditional system requires different numbers. Here are some basic conversions:

  • Inches to Feet: Divide the number of inches by 12 because there are 12 inches in 1 foot.
  • Feet to yards: Divide the number of feet by 3 because there are 3 feet in 1 yard.
  • Yards to Miles: Divide the number of yards by 1,760 because there are 1,760 yards in 1 mile.
Example: Convert 5280 feet to miles. Step 1: Convert feet to yards: 5280 ft ÷ 3 = 1,760 yds Step 2: Convert yards to miles: 1,760 yds ÷ 1,760 = 1 mi Therefore, 5,280 feet equals 1 mile.
Example: Convert 5280 feet to miles. Step 1: Convert feet to yards: 5280 ft ÷ 3 = 1,760 yds Step 2: Convert yards to miles: 1,760 yds ÷ 1,760 = 1 mi Therefore, 5,280 feet equals 1 mile.

Use of units of length in everyday life

Understanding and using units of length correctly is essential in many situations, such as building a house, buying clothes, or even in navigation. Here are some examples of how we use these units daily:

  • Measuring height: Typically, height is measured in meters or feet. For example, a person may be 1.75 meters or 5 feet 8 inches tall.
  • Buying fabric: Fabric is often sold by the meter or yard. If you want to buy enough fabric to make a dress, you could say you need 2 meters of fabric.
  • Travel distances: When driving, distances are often measured in kilometers or miles. You may think your destination is 50 kilometers or 30 miles away.
  • Building and construction: In construction, measurements need to be precise. You will often need to measure wood, metal rods and other materials using appropriate units such as meters or feet.

Practice problems

Let's practice what we've learned. Try solving these problems:

  1. If a pencil is 150 millimeters long, how many centimeters will it be?
  2. An amusement park is 3 kilometers wide. How many meters wide is it?
  3. If a rope is 25 feet long, what is its length in inches?
  4. The distance between two cities is 5 miles. How many yards is it?

Solution Explanation:

1. Convert 150 mm to cm: 150 mm ÷ 10 = 15 cm 2. Convert 3 km to meters: 3 km × 1,000 = 3,000 meters 3. Convert 25 feet to inches: 25 ft × 12 = 300 inches 4. Convert 5 miles to yards: 5 mi × 1,760 = 8,800 yards
1. Convert 150 mm to cm: 150 mm ÷ 10 = 15 cm 2. Convert 3 km to meters: 3 km × 1,000 = 3,000 meters 3. Convert 25 feet to inches: 25 ft × 12 = 300 inches 4. Convert 5 miles to yards: 5 mi × 1,760 = 8,800 yards

Conclusion

Understanding units of length is important in both science and everyday life. Knowing how to convert between different units of the same system ensures accuracy in measurements and helps with a wide range of tasks, from school work to practical tasks like cooking or construction. By giving meaningful quantities to objects and distances through measurement, you are able to better understand the world around you and make informed decisions. Continue to practice using units of length and converting, and soon you'll find them second nature.


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Units of Length

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