Class 4 Maths Chapter 6 Measuring Length – Revision Notes

Chapter 6, Measuring Length, covers standard length units (millimetres, centimetres, metres, kilometres), converting between them, and finding the perimeter of simple shapes. This revision guide covers all three parts of the chapter with worked examples.

Last Updated: September 23, 2026

Key Concepts

1 metre equals 100 centimetres, and 1 kilometre equals 1,000 metres. A centimetre is further divided into 10 millimetres. Small objects are usually measured in centimetres or millimetres, while larger distances are measured in metres or kilometres.

Perimeter is the total distance around a closed shape, found by adding the lengths of all its sides. It tells you how much fencing, ribbon, or boundary material would be needed to go exactly around the shape once.

Perimeter Formulas

• Perimeter of a rectangle = 2 × (length + breadth)
• Perimeter of a square = 4 × side
• Perimeter of any other closed shape = sum of the lengths of all its sides

Quick Recap

• 1 metre = 100 centimetres.
• 1 centimetre = 10 millimetres.
• 1 kilometre = 1,000 metres.
• Perimeter of a rectangle = 2 × (length + breadth).
• Perimeter of a square = 4 × side.
• Convert all lengths to the same unit before adding them to find a perimeter.

Worked Examples

Example 1: Find the perimeter of a rectangular garden that is 12 m long and 8 m wide.
Solution: Perimeter = 2 × (12 + 8) = 2 × 20 = 40 m.

Example 2: Find the perimeter of a square playground with a side of 15 m.
Solution: Perimeter = 4 × 15 = 60 m.

Example 3: A room’s length is 4 m 50 cm. What is this in centimetres?
Solution: 4 m = 400 cm. Total = 400 cm + 50 cm = 450 cm.

Example 4: A field has four unequal sides measuring 25 m, 18 m, 30 m and 20 m. What is its perimeter?
Solution: Perimeter = 25 + 18 + 30 + 20 = 93 m.

More Worked Examples

Example 5: A rectangular park is 50 m long and its perimeter is 160 m. What is its width?
Solution: Perimeter = 2 × (length + breadth), so 160 = 2 × (50 + breadth). Dividing both sides by 2: 80 = 50 + breadth, so breadth = 30 m.

Example 6: A pentagon-shaped garden has 5 equal sides, each 8 m long. What is its perimeter?
Solution: Perimeter = 5 × 8 = 40 m.

Real-Life Connections

Perimeter is exactly the measurement needed for fencing a plot, framing a photo, or putting a border of ribbon or lace around a piece of cloth. Length conversion, meanwhile, shows up when reading a tailor’s measuring tape (cm), a road distance sign (km), or a ruler at school (mm and cm) — connecting the chapter to things students already encounter regularly makes the units easier to remember.

Common Mistake to Avoid

A common mistake is adding measurements in different units without converting them first — for example, adding metres directly to centimetres gives a wrong total. Always convert every measurement to the same unit before adding. Another common mistake is confusing perimeter (a length, the distance around a shape) with area (how much surface it covers) — this chapter deals only with perimeter.

Practice Questions

1. Find the perimeter of a rectangle with length 9 m and breadth 6 m.
2. Find the perimeter of a square with side 7 cm.
3. Convert 6 m 20 cm to centimetres.
4. A triangular plot has sides 10 m, 12 m and 14 m. What is its perimeter?

Answers: 1. 2 × (9+6) = 30 m   2. 4 × 7 = 28 cm   3. 620 cm   4. 10+12+14 = 36 m

Frequently Asked Questions

Why do we use different units like cm and km for length instead of just one unit?
Using a single small unit like cm for very large distances, such as between two cities, would give unwieldy huge numbers, so bigger units like km keep large measurements easy to read and use.

Do all four sides need to be measured to find the perimeter of a rectangle?
No — since opposite sides of a rectangle are equal, you only need the length and the breadth; the formula 2 × (length + breadth) already accounts for both pairs of equal sides.

What is the difference between perimeter and length?
Length usually refers to one side or one straight measurement, while perimeter is the total distance around an entire closed shape — the sum of all its sides.

Why does the rectangle formula multiply by 2 instead of just adding all four sides?
Because a rectangle’s opposite sides are always equal, “2 × (length + breadth)” is a shortcut for adding length + breadth + length + breadth — it gives the same answer with less writing.

Can perimeter be found for shapes that aren’t rectangles or squares?
Yes — for any closed shape, simply add up the lengths of all its sides, whether it has 3, 4, 5, or more sides; the special formulas for rectangles and squares are just shortcuts for those two common shapes.

Full walkthrough: Chapter 6 Solutions · Extra Questions.

Written by Satish

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