Mensuration Class 8th – Easy Notes, Formulas, Tricks & Examples

Ever felt that mensuration questions twist your brain like a Rubik’s Cube? You’re not alone! Many Class 8 students find shapes, areas, and volumes confusing until they realise these concepts are everywhere around us, from painting a wall to wrapping a gift box. 

This blog makes mensuration easy with real-life examples, clear formulas, solved questions, and step-by-step methods. Whether it’s 2D shapes or 3D solids, every idea will make sense here. And at the end, see how PlanetSpark’s expert-led maths course makes learning fun and fearless for students through interactive, concept-based lessons.

What Is Mensuration? – Understanding the Basics

In simple terms, mensuration means measuring. It deals with the measurement of geometric figures and shapes—both flat (2D) and solid (3D).
Mensuration helps in finding length, area, perimeter, volume, and surface area of different shapes.

It’s not just a topic in maths; it’s a life skill.

• When a painter estimates how much paint is needed for a wall that’s mensuration.

• When an engineer calculates the material for a tank that’s mensuration too.
  So, mensuration connects mathematics with real life, helping students develop logical thinking and spatial awareness.

Key Terms in Mensuration You Should Know

Before learning the formulas, it’s important to understand some basic terms used in mensuration class 8th:

These terms build the foundation for class 8 mensuration. Once they’re clear, every problem becomes easier to visualise and solve.

Units of Measurement Used in Mensuration

Mensuration deals with different units of measurement, depending on what is being calculated.

For Length and Perimeter:

• millimetre (mm)

• centimetre (cm)

• metre (m)

• kilometre (km)

For Area:

• square centimetre (cm²)

• square metre (m²)

• square kilometre (km²)

For Volume:

• cubic centimetre (cm³)

• cubic metre (m³)

• litre (L)

Conversion Tips:

• 1 m = 100 cm

• 1 m² = 10,000 cm²

• 1 m³ = 10,00,000 cm³

• 1 L = 1000 cm³

Understanding units ensures accuracy most mistakes in mensuration class 8th occur because of missed conversions!

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2D Shapes and Their Formulas (Perimeter and Area)

Two-dimensional (2D) shapes are flat figures that have length and breadth, but no depth.
Let’s explore the key 2D shapes covered in class 8 mensuration.

1. Rectangle

📘 Example:
A rectangle has length = 8 cm and breadth = 6 cm.
Area = 8 × 6 = 48 cm², Perimeter = 2 × (8 + 6) = 28 cm.

2. Square

📘 Example:
If a square’s side is 5 cm,
Area = 5² = 25 cm², Perimeter = 4 × 5 = 20 cm.

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3. Triangle

📘 Example:
For a triangle with base 8 cm and height 5 cm,
Area = ½ × 8 × 5 = 20 cm².

4. Parallelogram

📘 Example:
A parallelogram with base 7 cm and height 4 cm has
Area = 7 × 4 = 28 cm².

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5. Trapezium

📘 Example:
For a trapezium with sides 6 cm, 10 cm and height 4 cm:
Area = ½ × (6 + 10) × 4 = 32 cm².

6. Circle

📘 Example:
For a circle of radius 7 cm,
Circumference = 2 × 22/7 × 7 = 44 cm,
Area = 22/7 × 7 × 7 = 154 cm².

3D Shapes and Their Formulas (Surface Area and Volume)

Three-dimensional shapes have length, breadth, and height. They occupy space and have volume and surface area. Let’s look at the important 3D shapes in class 8 mensuration.

1. Cube

📘 Example:
If side = 5 cm,
TSA = 6 × 25 = 150 cm², Volume = 125 cm³.

2. Cuboid

📘 Example:
If length = 8 cm, breadth = 6 cm, height = 5 cm,
Volume = 8 × 6 × 5 = 240 cm³.

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3. Cylinder

📘 Example:
If radius = 7 cm and height = 10 cm,
Volume = 22/7 × 7 × 7 × 10 = 1540 cm³.

4. Cone

📘 Example:
For radius = 3 cm, height = 4 cm,
l = 5 cm, Volume = ⅓ × 3.14 × 9 × 4 = 37.68 cm³.

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5. Sphere

📘 Example:
For radius = 3 cm,
Volume = 4/3 × 3.14 × 27 = 113.04 cm³.

6. Hemisphere

📘 Example:
If radius = 7 cm,
Volume = ⅔ × 22/7 × 7 × 7 × 7 = 718.67 cm³.

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Mensuration Class 8 Formula List (All in One Place)

Here’s your ultimate quick reference chart for mensuration class 8th formulas 👇

Keep this table handy—it’s your go-to sheet before every test or quick revision.

How to Derive Mensuration Class 8 Formulas Step by Step

Deriving formulas helps understanding far more than rote memorisation. Below are clear, step-by-step derivations for the most important mensuration class 8th formulas explained visually (words instead of pictures), using simple logic, and with quick memory hints at the end of each derivation.

1. Area of a Rectangle — base idea

A rectangle’s area equals the number of unit squares that fit inside it.

1. Take a rectangle with length l and breadth b.

2. Imagine dividing it into rows: each row has l unit squares and there are b such rows (if units are whole).

3. Total number of unit squares = l × b.

4. So, Area = l × b.

Memory hint: Rectangle = length × breadth — think of a grid of rows × columns.

2. Area of a Triangle — half of a rectangle/parallelogram

A triangle is half of a parallelogram whose base and height match the triangle’s base and height.

1. Consider a triangle with base b and height h.

2. Duplicate the triangle and place the copy next to it so their heights match and bases align — together they form a parallelogram with base b and height h.

3. Area of that parallelogram = base × height = b × h.

4. The triangle is half the parallelogram, so Area (triangle) = ½ × b × h.

Memory hint: Two equal triangles = one parallelogram → area gets halved.

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3. Area of a Parallelogram — rearrangement

A parallelogram is basically a slanted rectangle; cutting and rearranging shows the area equals base × height.

1. Take a parallelogram with base b and perpendicular height h.

2. Slice a small triangle from one end and move it to the other; the shape becomes a rectangle of width b and height h.

3. Area of that rectangle = b × h.

4. Therefore, Area (parallelogram) = b × h.

Memory hint: Parallelogram → rearrange into a rectangle.

4. Area of a Trapezium (Trapezoid) — average of parallel sides

A trapezium has two parallel sides of lengths a and b and height h.

1. Visualise two identical trapeziums arranged to form a parallelogram: placing one upside-down next to the other aligns the parallel sides so the new base = (a + b) and height = h.

2. Area of this parallelogram = (a + b) × h.

3. Since the parallelogram consists of two trapeziums, Area (one trapezium) = ½ × (a + b) × h.

Memory hint: Take the average of the two parallel sides, multiply by height: ½(a+b)h.

5. Circumference and Area of a Circle — using limits and rearrangement

A circle’s area and circumference come from thinking of it as many tiny sectors (pizza slices).

Circumference (intuitive):

• The circumference is the length around the circle. If radius = r, the commonly used constant π relates diameter to circumference: Circumference = 2πr. (Think of wrapping the circle once — the length scales with radius.)

Area (sector rearrangement method):

1. Cut the circle into many narrow equal sectors (like many pizza slices).

2. Rearrange alternate slices (one up, one down) to form a shape that approximates a rectangle as the number of sectors increases.

   • The rectangle’s height ≈ r (the radius).

   • The rectangle’s base ≈ half the circumference = ½ × 2πr = πr.

3. Area of rectangle ≈ base × height = πr × r = πr².

4. Thus Area (circle) = πr².

Memory hint: Circle area = π × radius²; think of circle ≈ rectangle of width πr and height r.

6. Volume of a Cylinder — stack of circles

A cylinder looks like a stack of circular discs.

1. Each cross-sectional disc perpendicular to the height has area πr².

2. If the cylinder’s height = h, stacking h units of such discs gives total volume = base area × height = πr² × h.

3. So Volume (cylinder) = πr²h.

Memory hint: Volume = area of base × height.

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7. Volume of a Cone — one-third of a cylinder

A cone with the same base and height as a cylinder occupies one-third the cylinder’s volume (can be shown by calculus or by dissection arguments).

1. Consider a cone and a cylinder with the same base radius r and height h.

2. Through calculus or careful geometric dissection/volume-filling experiments, the cone fills exactly one-third of the cylinder.

3. Since cylinder volume = πr²h, Volume (cone) = ⅓ × πr²h.

Memory hint: Cone = (1/3) × cylinder with same base and height.

8. Volume of a Sphere — relation to radius

Deriving the sphere volume rigorously needs calculus (integration), but an intuitive idea uses comparison with cones and cylinders (Archimedes’ method):

1. Archimedes showed that the volume of a sphere of radius r equals the volume of a cylinder (of radius r and height 2r) minus the volume of a cone-like complement; this leads to Volume = 4/3 × πr³.

2. Accepting the classical derivation (or using integral calculus), obtain Volume (sphere) = ⁴⁄₃πr³.

Memory hint: Sphere volume grows with cube of radius; coefficient 4/3 × π.

9. Surface Area of a Cylinder — curved area + ends

A cylinder’s total surface area includes the curved area around plus top and bottom circles.

1. Curved Surface Area (CSA): unwrap the curved surface — it becomes a rectangle with height h and width equal to the circumference 2πr, so CSA = 2πr × h = 2πrh.

2. Two circular ends each have area πr², so combined area = 2πr².

3. Total Surface Area (TSA) = CSA + area of ends = 2πrh + 2πr² = 2πr(r + h).

Memory hint: Unwrap the shell (curved part) into a rectangle.

10. Surface Area of a Cone — using slant height

A cone’s curved surface when unwrapped becomes a sector of a circle.

1. Slant height = l = √(r² + h²) (Pythagoras on right triangle formed by radius, height, slant).

2. The curved surface becomes a circular sector whose arc length equals the base circumference 2πr and whose radius equals l.

3. Area of this sector = ½ × (arc length) × radius = ½ × (2πr) × l = πrl.

4. Add base area πr² for total surface area πr(l + r).

Memory hint: Curved surface = πrl.

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11. Surface Area of Sphere — from scaling arguments

For a sphere of radius r, the surface area equals 4πr². A heuristic view:

1. As radius grows, surface area scales with the square of radius (units of area).

2. The constant 4π arises from calculus or by considering limits of polygons approximating spheres; rigorous derivation uses surface integrals.

3. Result: Surface Area (sphere) = 4πr².

Memory hint: Sphere surface = 4 × area of circle with same radius.

12. Volume and Surface Area of Cube and Cuboid — counting faces

Cube (side a):

• TSA = 6 faces × area of each square = 6a².

• Volume = side³ = a³.

Cuboid (l, b, h):

• TSA = 2(lb + bh + hl) — sum of areas of three distinct face pairs multiplied by 2.

• Volume = l × b × h.

Memory hint: Count faces (6) and multiply by each face area

How to Solve Complex Mensuration Class 8 Problems Easily 

Solving complex mensuration problems can feel tricky at first, but with the right approach and a few smart tricks, you can turn them into easy wins. 

Here are some simple and effective tips to help you master mensuration class 8th questions quickly and confidently:

1. Understand the Shape Before Using Any Formula

Always visualise the figure whether it’s a cube, cone, or combination of shapes.
Identify known parameters (length, radius, height, etc.).
Check if it’s a 2D (area) or 3D (volume/surface area) question before choosing a formula.

2. Draw a Neat Diagram

A clear, labelled diagram helps you understand hidden dimensions or missing measurements.
When solving combined shapes, sketch separate parts first (like a cylinder plus cone).

3. Write Down the Given and Required Values

List what’s given (e.g., radius = 7 cm, height = 10 cm).
Then clearly note what you have to find (like total surface area or curved surface area).
This reduces confusion in multi-step problems.

4. Break Down Compound Shapes

Many complex mensuration questions combine two or more solids.
Divide them into known shapes (like cuboid + half-sphere).
Solve for each separately and then add or subtract as required.

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5. Use Standard Mensuration Formulas Confidently

Revise key formulas regularly for quick recall.
Group them logically:

• 2D figures – Rectangle, Triangle, Circle, Trapezium

• 3D figures – Cube, Cuboid, Cylinder, Cone, Sphere
  Remember: Volume = space inside, Surface area = outer covering.

6. Keep Units Consistent

Convert all measurements to the same unit before solving (cm, m, etc.).
Always express final answers with correct units (cm² for area, cm³ for volume).

7. Use Shortcut Ratios and Relations

Cylinder vs Cone (same base and height): Cone volume = ⅓ of cylinder.
Sphere vs Cylinder: Sphere volume = ⅔ of cylinder (same diameter and height).
These relations help when comparing or subtracting volumes quickly.

 8. Memorise Through Derivations, Not Rote Learning

Understand why formulas work it helps recall them easily.
For example, remember a triangle’s area is half of a parallelogram.

9. Check for Hidden Dimensions or Missing Data

Some problems hide details within the question, e.g., “Find the area of metal used in making an open cylinder.”
Understand what’s excluded (like open top or hollow part).

10. Always Cross-Check the Answer

Recalculate using estimated values does your answer seem reasonable?
Double-check units and decimal placements before finalising.

Tips to Remember Mensuration Class 8 Formulas Easily

1. Group similar shapes:
   – Circle, cone, and sphere use π.

2. Use mnemonics:
   – “Tall Cylinders Hold Pie” → TCHP → TSA, CSA, Height, πr²h

3. Create patterns:
   – Cube & Cuboid both have formulas with “6” and “2” multipliers.

4. Write daily:
   – Revising 5 formulas daily makes a big difference.

5. Connect with real-life:
   – Think of your pencil box as a cuboid or ball as a sphere!

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Mensuration Tricks and Shortcuts for Quick Calculation

Struggling to remember all those formulas? Don’t worry Mensuration doesn’t have to be a memory marathon! With a few smart tricks and shortcuts, you can solve questions faster and score higher. 

Let’s decode them:

1. Formula Memorisation Hacks

• Visualise Shapes: Don’t just mug up formulas — see the shapes in your mind. For example, a rectangle’s area is length × breadth because it’s like filling small squares across its surface!

• Use Mnemonics:

  • C²A³ → Circle = Circumference 2πr, Area πr², 3D (Sphere) Volume 4/3πr³

  • “L × B × H” = Box’s Strength — Remember this for cuboids and cubes.

• Flashcards & Sticky Notes: Write one formula per card and stick them near your study area. Quick glance = instant recall!

• Group Similar Formulas: Keep all 2D (area, perimeter) together and 3D (volume, surface area) in another list to avoid confusion.

2. Calculation Shortcuts

• Use 22/7 for π Instead of 3.14 – It’s more accurate and easier to multiply mentally.

• Convert Units Early: If the question mixes cm and m, convert at the start to avoid messy decimals.

• Round Smartly: When dealing with decimals like 43.96 cm, round it to 44 cm for quick estimation in MCQs.

• Square and Cube Tips:

  • (a + b)² = a² + 2ab + b² — helps when sides are slightly different.

  • Learn squares and cubes up to 20 by heart — it saves loads of time!

• Visual Estimation: Before calculating, quickly guess the answer range. It helps catch silly mistakes if your final number seems off.

 Pro Tip:

Every time you solve a Mensuration problem, note the formula on top and underline the unit in your final answer. This trains your memory naturally no extra effort needed!

Turn boring maths into exciting logic games!

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Some Solved Examples of Mensuration Class 8

Let’s solve a few examples together so you get a clear idea of how to handle different shapes:

Example 1:
Find the area of a rectangle with length 10 cm and breadth 6 cm.
Solution:
Area = length × breadth = 10 × 6 = 60 cm²

Example 2:
A circle has a radius of 7 cm. Find its circumference.
Solution:
Circumference = 2πr = 2 × 3.14 × 7 = 43.96 cm

Example 3:
Find the volume of a cube with side 5 cm.
Solution:
Volume = side³ = 5³ = 125 cm³

Example 4:
A cylinder has radius 3 cm and height 10 cm. Find its volume.
Solution:
Volume = πr²h = 3.14 × 3² × 10 = 282.6 cm³

These examples show how simple formulas can help you quickly find the area or volume of almost any 2D or 3D shape.

Common Mistakes Students Make in Mensuration

Even confident learners sometimes slip up! Here are a few common mistakes to watch out for:

1. Mixing up units – Using cm for one side and m for another can make answers wrong. Always keep units consistent.

2. Forgetting the formula – Many students confuse perimeter and area formulas, especially for triangles and circles.

3. Ignoring decimals or rounding – Mensuration often involves π (3.14). Be careful while rounding!

4. Skipping diagram labelling – Without a neat diagram, it’s easy to misread dimensions.

5. Not writing units in the final answer – Always end your answer with the correct unit (cm², m³, etc.).

✅ Tip: Before your exams, make a “Formula Flash Sheet” to revise all mensuration formulas in one go!

How PlanetSpark Makes Maths Fun & Easy

At PlanetSpark, learning isn’t about memorising formulas it’s about understanding concepts in a creative way!

Here’s how we help students master topics like Mensuration (Class 8):

• Interactive Visual Learning: Our lessons use 3D shapes, animations, and fun examples that bring maths to life.

• Practice Through Play: Students learn formulas using real-life objects and challenges, not just theory.

• Confidence Building: Every student gets personalised feedback and guidance from certified tutors.

• Result-Oriented Learning: We help you understand the “why” behind every formula so you can solve any question confidently.

Master Maths Calculations with Confidence

Mensuration isn’t just about shapes and formulas it’s about seeing maths all around you! Whether you’re measuring your classroom board, calculating your desk’s area, or understanding how much space your backpack occupies, Mensuration makes maths practical and fun.

So, keep practising, stay curious, and remember the more you play with numbers, the more confident you’ll become!