📦 Volume of Prisms

Cambridge Lower Secondary · Grade 7 · Geometry & Measure

Cuboid (Rectangular Prism)
V = l × w × h
e.g. 5 × 4 × 3 = 60 cm³
Triangular Prism
V = ½ × b × h × l
e.g. ½ × 6 × 4 × 10 = 120 cm³
Cylinder
V = πr²h
e.g. π × 3² × 8 ≈ 226.2 cm³

Volume = layers stacked up! Watch a cuboid fill with water 💧

Volume: 0 cm³ / 120 cm³

What you'll learn:

  • Volume = cross-sectional area × length (the core idea)
  • Volume of a cuboid: V = l × w × h
  • Volume of a triangular prism: V = ½ × b × h × l
  • Volume of a cylinder: V = πr²h
  • Unit conversions: cm³ ↔ m³, ml ↔ cm³
  • Finding a missing dimension when volume is given
  • Real-world contexts: fish tanks, swimming pools, pipes

📖 Learn: Volume of Prisms

Part 1: What is Volume?

Volume is the amount of 3D space an object occupies. We measure it in cubic units — cm³, m³, mm³.

📌 Key idea: Volume = cross-sectional area × length
Think of a prism as a stack of identical cross-sections. The area of the face × how long you stretch it = total volume.
A cube with side 1 cm has volume = 1 × 1 × 1 = 1 cm³. That is our unit.
💡 Just like area counts squares, volume counts cubes!

Part 2: Volume of a Cuboid

A cuboid (rectangular prism) has a rectangular cross-section.

📌 Formula: V = l × w × h
Why? Cross-section area = l × w, then multiply by height h.
Example: A box 8 cm × 5 cm × 3 cm → V = 8 × 5 × 3 = 120 cm³
Example: A fish tank 40 cm × 20 cm × 25 cm → V = 40 × 20 × 25 = 20 000 cm³ = 20 litres
💡 1 cm³ = 1 ml, so 20 000 cm³ = 20 000 ml = 20 litres.

Part 3: Volume of a Triangular Prism

A triangular prism has a triangular cross-section.

📌 Cross-section area = ½ × base × height (of the triangle)
📌 Volume: V = ½ × b × h × l where l is the length of the prism
Example: Triangle base = 6 cm, triangle height = 4 cm, prism length = 10 cm
V = ½ × 6 × 4 × 10 = ½ × 240 = 120 cm³
💡 Identify the triangular face first — its base and height belong to the triangle, not the prism's length.

Part 4: Volume of a Cylinder

A cylinder is a circular prism. Its cross-section is a circle.

📌 Cross-section area = πr²
📌 Volume: V = πr²h
Example: r = 5 cm, h = 12 cm → V = π × 25 × 12 = 300π ≈ 942.5 cm³
Finding r from diameter: if d = 8 cm, then r = 4 cm.
💡 Leave answers in terms of π where possible (e.g., 300π cm³) unless told to use π ≈ 3.14 or the π key.

Part 5: Unit Conversions & Finding Missing Dimensions

Volume unit conversions:

1 m = 100 cm → 1 m³ = 100 × 100 × 100 = 1 000 000 cm³
1 cm³ = 1 ml → 1 litre = 1000 ml = 1000 cm³
1 m³ = 1 000 000 ml = 1000 litres

Finding a missing dimension:

If V = 240 cm³, l = 8 cm, w = 5 cm — find h.
240 = 8 × 5 × h → 240 = 40h → h = 240 ÷ 40 = 6 cm
If V = 150π cm³, r = 5 cm — find h. → 150π = π × 25 × h → h = 150 ÷ 25 = 6 cm
💡 Divide volume by the area of the cross-section to find the missing length!

💡 Worked Examples

Example 1: Volume of a Cuboid

A storage box is 15 cm long, 10 cm wide and 8 cm tall. Find its volume.

Step 1: Write the formula: V = l × w × h
Step 2: Substitute: V = 15 × 10 × 8
Step 3: Calculate: 15 × 10 = 150, then 150 × 8 = 1200
Answer: V = 1200 cm³
✅ Check: units must be cubic (cm³). If dimensions were in m, answer would be in m³.

Example 2: Volume of a Triangular Prism

A triangular prism has a triangular cross-section with base 9 cm and perpendicular height 6 cm. The prism is 14 cm long. Find its volume.

Step 1: Find the cross-section area: A = ½ × b × h = ½ × 9 × 6 = 27 cm²
Step 2: Multiply by prism length: V = 27 × 14 = 378 cm³
🔺 Always use the perpendicular height of the triangle, not the slant side.

Example 3: Volume of a Cylinder

A cylindrical pipe has diameter 12 cm and length 50 cm. Calculate its volume. Give your answer in terms of π.

Step 1: Find radius: r = 12 ÷ 2 = 6 cm
Step 2: Write formula: V = πr²h = π × 6² × 50
Step 3: Calculate: 6² = 36, then 36 × 50 = 1800
Answer: V = 1800π cm³ ≈ 5654.9 cm³

Example 4: Finding a Missing Dimension

A cuboid has volume 360 cm³. Its length is 12 cm and its width is 5 cm. Find its height.

Step 1: Write formula: V = l × w × h → 360 = 12 × 5 × h
Step 2: Simplify: 360 = 60 × h
Step 3: Solve: h = 360 ÷ 60 = 6 cm
🔍 V ÷ (l × w) = h. Think of it as: if you know the base area and the total volume, dividing gives the height.

🎨 Visualizer

💧 Fill It Up — Water Level Animation

Drag the slider to fill the cuboid. Watch each layer stack up to build the total volume!

5 cm
4 cm
0 cm

Volume filled: 0.0 cm³  |  Max: 160.0 cm³

📌 Each 1 cm rise in water = adding one layer of l × w = 20 cm² of cubes!

🏗️ Prism Builder — Pick Your Shape!

Choose a cross-section, set the dimensions with sliders, and see the volume calculate live.

🔬 Unit Conversion Visualiser

One 1 m³ cube contains exactly 1 000 000 cm³. Watch the zoom animation!

1 m³ cube
1 m = 100 cm
1 m³ = 1 000 000 cm³
1 cm³ = 1 ml

🐠 Fish Tank Capacity Calculator

Enter your fish tank dimensions to find the volume, convert to litres, and discover how many fish can live in it!

Length (cm)
×
Width (cm)
×
Height (cm)
🐟 Fun rule: 1 fish needs at least 5 litres of water to be happy and healthy!

✏️ Exercise 1: Volume of Cuboids

Calculate the volume of each cuboid. Give units in your answer.

1. l = 6 cm, w = 4 cm, h = 5 cm  →  V =
2. l = 10 cm, w = 3 cm, h = 7 cm  →  V =
3. l = 8 cm, w = 8 cm, h = 8 cm (cube)  →  V =
4. l = 15 cm, w = 6 cm, h = 4 cm  →  V =
5. l = 2.5 cm, w = 4 cm, h = 6 cm  →  V =
6. l = 12 m, w = 5 m, h = 3 m  →  V =
7. l = 0.5 m, w = 0.4 m, h = 0.2 m  →  V =
8. A swimming pool: 25 m × 10 m × 2 m  →  V =

✏️ Exercise 2: Volume of Triangular Prisms

V = ½ × b × h × l   (b and h are the base and height of the triangle; l is the prism length)

1. b = 4 cm, h = 3 cm, l = 10 cm  →  V =
2. b = 6 cm, h = 5 cm, l = 8 cm  →  V =
3. b = 10 cm, h = 6 cm, l = 12 cm  →  V =
4. b = 7 cm, h = 4 cm, l = 15 cm  →  V =
5. b = 9 cm, h = 8 cm, l = 20 cm  →  V =
6. b = 3 m, h = 2.5 m, l = 6 m  →  V =
7. b = 12 cm, h = 5 cm, l = 25 cm  →  V =
8. A triangular roof section: b = 4 m, h = 1.5 m, l = 10 m  →  V =

✏️ Exercise 3: Volume of Cylinders

V = πr²h   Use π ≈ 3.14159 (or the π key). Round to 1 d.p. unless stated.

1. r = 3 cm, h = 10 cm  →  V = (1 d.p.)
2. r = 5 cm, h = 8 cm  →  V = (1 d.p.)
3. d = 10 cm (diameter), h = 6 cm  →  V = (1 d.p.)
4. r = 7 cm, h = 15 cm  →  V = (1 d.p.)
5. r = 2 m, h = 5 m  →  V = (1 d.p.)
6. d = 14 cm (diameter), h = 20 cm  →  V = (1 d.p.)
7. A cylindrical can: r = 4 cm, h = 12 cm  →  V = (1 d.p.)
8. A pipe: r = 0.5 m, h = 3 m  →  V = (2 d.p.)

🔍 Exercise 4: Find the Missing Dimension

Use V = l × w × h or V = ½bhl or V = πr²h rearranged to find the unknown.

1. Cuboid: V = 120 cm³, l = 6 cm, w = 4 cm. Find h =
2. Cuboid: V = 360 cm³, l = 10 cm, w = 6 cm. Find h =
3. Cuboid: V = 240 cm³, l = 8 cm, h = 5 cm. Find w =
4. Triangular prism: V = 90 cm³, b = 6 cm, h = 5 cm. Find l =
5. Triangular prism: V = 168 cm³, b = 8 cm, l = 14 cm. Find h =
6. Cylinder: V = 200π cm³, r = 5 cm. Find h =
7. Cylinder: V = 192π cm³, h = 12 cm. Find r =
8. Cuboid room: V = 96 m³, floor 8 m × 6 m. Find ceiling height =

🌍 Exercise 5: Units & Real-World Contexts

1. Convert 2 500 000 cm³ to m³ =
2. Convert 0.35 m³ to cm³ =
3. Convert 4500 cm³ to litres =
4. A fish tank: 50 cm × 25 cm × 30 cm. Volume in cm³ =
5. Same tank: Volume in litres =
6. A swimming pool: 30 m × 12 m × 1.8 m. Volume in m³ =
7. Same pool: Volume in litres (1 m³ = 1000 L) =
8. A cylindrical water tank: r = 0.6 m, h = 1.5 m. Volume in litres (1 d.p.) =

📝 Practice: 20 Mixed Questions

All types mixed. Round decimals to 1 d.p. unless stated.

🏆 Challenge: 8 Hard Questions

Multi-step, reasoning, and problem-solving. Show your working!

C1. A cylinder and a cuboid have the same volume. The cuboid is 10 cm × 8 cm × 6 cm. The cylinder has radius 4 cm. Find the height of the cylinder to 2 d.p.

h =

C2. A triangular prism has volume 270 cm³. The triangular face has base 9 cm. The prism length is 12 cm. Find the perpendicular height of the triangle.

h =

C3. A fish tank (cuboid) holds exactly 120 litres when full. Its base measures 50 cm × 40 cm. Find the height of the tank in cm.

h =

C4. A large cube has side length 1 m. It is cut into small cubes each with side length 5 cm. How many small cubes are made?

Number =

C5. A swimming pool is 20 m long, 8 m wide, and has a sloped floor. One end is 1 m deep, the other is 2.5 m deep. The cross-section is a trapezium. Find the volume in m³.
(Area of trapezium = ½(a + b)h, where a and b are the parallel sides)

V =

C6. Two cylinders: Cylinder A has r = 3 cm, h = 8 cm. Cylinder B has r = 6 cm, h = 2 cm. Which has the greater volume and by how much? (give exact answer in terms of π)

Difference = × π cm³ (enter the number only)

C7. A solid metal cuboid (8 cm × 6 cm × 5 cm) is melted and recast into a cylinder of radius 4 cm. Find the height of the cylinder to 2 d.p.

h =

C8. A cuboid box measures 30 cm × 20 cm × 15 cm. Small cubes each with volume 125 cm³ are packed inside. How many cubes fit, and what percentage of the box volume is filled?

Number of cubes =
% filled =